From ca74d1dd73dc0e106bed41449297669b111778ad Mon Sep 17 00:00:00 2001
From: "Timur A. Fatkhullin" <timur@sao.ru>
Date: Mon, 18 Aug 2025 12:22:45 +0300
Subject: [PATCH] ...

---
 mcc/CMakeLists.txt  |   2 +-
 mcc/mcc_angle.h     | 532 ++++++++++++++++++++++++++++++++++++++++++++
 mcc/mcc_ccte_erfa.h | 468 ++++++++++++++++++++++++++++++--------
 mcc/mcc_generics.h  |  43 ++--
 mcc/mcc_pzone.h     |  78 +++++++
 5 files changed, 1007 insertions(+), 116 deletions(-)
 create mode 100644 mcc/mcc_angle.h
 create mode 100644 mcc/mcc_pzone.h

diff --git a/mcc/CMakeLists.txt b/mcc/CMakeLists.txt
index 6279612..9ef4230 100644
--- a/mcc/CMakeLists.txt
+++ b/mcc/CMakeLists.txt
@@ -65,7 +65,7 @@ include_directories(${ERFA_INCLUDE_DIR})
 
 
 
-set(MCC_LIBRARY_SRC1 mcc_generics.h mcc_defaults.h mcc_traits.h mcc_utils.h mcc_ccte_iers.h mcc_ccte_iers_default.h)
+set(MCC_LIBRARY_SRC1 mcc_generics.h mcc_defaults.h mcc_traits.h mcc_utils.h mcc_ccte_iers.h mcc_ccte_iers_default.h mcc_ccte_erfa.h)
 set(MCC_LIBRARY1 mcc1)
 add_library(${MCC_LIBRARY1} INTERFACE ${MCC_LIBRARY_SRC1})
 target_compile_features(${MCC_LIBRARY1} INTERFACE cxx_std_23)
diff --git a/mcc/mcc_angle.h b/mcc/mcc_angle.h
new file mode 100644
index 0000000..ec253d0
--- /dev/null
+++ b/mcc/mcc_angle.h
@@ -0,0 +1,532 @@
+#pragma once
+
+#include "mcc_traits.h"
+#include "mcc_utils.h"
+
+constexpr double operator""_rads(long double val)  // angle in radians (no conversion)
+{
+    return val;
+}
+
+constexpr double operator""_degs(long double val)  // angle in degrees
+{
+    return val * std::numbers::pi / 180.0;
+}
+
+constexpr double operator""_arcmins(long double val)  // angle in arc minutes
+{
+    return val * std::numbers::pi / 180.0 / 60.0;
+}
+
+constexpr double operator""_arcsecs(long double val)  // angle in arc seconds
+{
+    return val * std::numbers::pi / 180.0 / 3600.0;
+}
+
+constexpr double operator""_dms(const char* s, size_t size)  // as a string "DEGREES:MINUTES:SECONDS"
+{
+    auto res = mcc::utils::parsAngleString(std::span{s, size});
+    if (res.has_value()) {
+        return res.value() * std::numbers::pi / 180.0;
+    } else {
+        throw std::invalid_argument("invalid sexagesimal representation");
+    }
+}
+
+constexpr double operator""_hms(const char* s, size_t len)  // as a string "HOURS:MINUTES:SECONDS"
+{
+    auto res = mcc::utils::parsAngleString(std::span{s, len}, true);
+    if (res.has_value()) {
+        return res.value() * std::numbers::pi / 180.0;
+    } else {
+        throw std::invalid_argument("invalid sexagesimal representation");
+    }
+}
+
+
+namespace mcc
+{
+
+/*  MCC-LIBRARY COORDINATES REPRESENTATION DEFINITIONS AND CLASS   */
+
+
+
+// tags for MccAngle class construction
+
+struct MccRadianTag {
+};
+struct MccDegreeTag {
+};
+static constexpr MccDegreeTag mcc_degrees{};
+struct MccHMSTag {
+};
+static constexpr MccHMSTag mcc_hms{};
+
+
+class MccAngle
+{
+protected:
+    double _angleInRads{0.0};
+    int _precision{2};
+
+public:
+    enum norm_kind_t {
+        NORM_KIND_0_360,    // [0,360]
+        NORM_KIND_0_180,    // [0,180]
+        NORM_KIND_180_180,  // [-180,180]
+        NORM_KIND_90_90,    // [-90,90]
+    };
+
+    MccAngle() = default;
+
+    // by default angle is in radians
+    // MccAngle(std::convertible_to<double> auto const& val, const MccRadianTag = MccRadianTag{}) : _angleInRads(val) {}
+
+    // construct angle in degrees, e.g.:
+    //     auto ang = MccAngle{180.0, mcc_degrees};
+    // MccAngle(std::convertible_to<double> auto const& val, const MccDegreeTag)
+    // {
+    //     _angleInRads = val * utils::deg2radCoeff;
+    // }
+
+    // by default angle is in radians
+    // template <typename T>
+    // MccAngle(const T& val, const MccRadianTag = MccRadianTag{})
+    //     requires std::is_arithmetic_v<T>
+    //     : _angleInRads(val)
+    // {
+    // }
+
+    // // construct angle in degrees, e.g.:
+    // //     auto ang = MccAngle{180.0, mcc_degrees};
+    // template <typename T>
+    // MccAngle(const T& val, const MccDegreeTag)
+    //     requires std::is_arithmetic_v<T>
+    //     : _angleInRads(val * utils::deg2radCoeff)
+    // {
+    // }
+
+
+    // by default angle is in radians
+    constexpr MccAngle(const double& val, const MccRadianTag = MccRadianTag{}) : _angleInRads(val) {}
+
+    // construct angle in degrees, e.g.:
+    //     auto ang = MccAngle{180.0, mcc_degrees};
+    constexpr MccAngle(const double& val, const MccDegreeTag) : _angleInRads(val * utils::deg2radCoeff) {}
+
+
+
+    // constuct angle from sexagesimal representation or floating-point number of degrees, e.g.:
+    //     auto ang = MccAngle{"-12:34:56.789"}; // from degrees:minutes:seconds
+    //     auto ang = MccAngle{"123.574698"}; // from degrees
+    constexpr MccAngle(traits::mcc_input_char_range auto const& val)
+    {
+        auto res = utils::parsAngleString(val);
+        if (res.has_value()) {
+            _angleInRads = res.value() * utils::deg2radCoeff;
+        } else {
+            throw std::invalid_argument("invalid sexagesimal representation");
+        }
+    }
+
+    // construct angle from sexagesimal representation or floating-point number of degrees, e.g.:
+    //     auto ang = MccAngle{"01:23:45.6789", mcc_hms}; // from hours:minutes:seconds
+    //     auto ang = MccAngle{"123.574698"}; // from degrees
+    constexpr MccAngle(traits::mcc_input_char_range auto const& val, const MccHMSTag)
+    {
+        auto res = utils::parsAngleString(val, true);
+        if (res.has_value()) {
+            _angleInRads = res.value() * utils::deg2radCoeff;
+        } else {
+            throw std::invalid_argument("invalid sexagesimal representation");
+        }
+    }
+
+    virtual ~MccAngle() = default;
+
+    template <std::derived_from<MccAngle> T>
+    constexpr auto& operator=(this T&& self, const T& other)
+    {
+        std::forward<decltype(self)>(self)._angleInRads = other._angleInRads;
+
+        return self;
+    }
+
+    template <std::derived_from<MccAngle> T>
+    constexpr auto& operator=(this T&& self, T&& other)
+    {
+        std::forward<decltype(self)>(self)._angleInRads = std::move(other._angleInRads);
+
+        return self;
+    }
+
+    template <typename T>
+    constexpr auto& operator=(this auto&& self, const T& val)
+        requires std::is_arithmetic_v<T>
+    {
+        std::forward<decltype(self)>(self)._angleInRads = val;
+
+        return self;
+    }
+
+    // normalize coordinate
+    template <norm_kind_t KIND>
+    MccAngle& normalize()
+    {
+        _angleInRads = std::fmod(_angleInRads, std::numbers::pi * 2.0);
+
+        if constexpr (KIND == NORM_KIND_0_360) {
+            if (_angleInRads < 0.0) {
+                _angleInRads += 2.0 * std::numbers::pi;
+            }
+        } else if constexpr (KIND == NORM_KIND_0_180) {
+            if (_angleInRads < -std::numbers::pi) {
+                _angleInRads = 2.0 * std::numbers::pi + _angleInRads;
+            } else if (_angleInRads < 0.0) {
+                _angleInRads = -_angleInRads;
+            }
+        } else if constexpr (KIND == NORM_KIND_180_180) {
+            if (_angleInRads > std::numbers::pi) {
+                _angleInRads = 2.0 * std::numbers::pi - _angleInRads;
+            } else if (_angleInRads < -std::numbers::pi) {
+                _angleInRads += 2.0 * std::numbers::pi;
+            }
+        } else if constexpr (KIND == NORM_KIND_90_90) {
+            if (_angleInRads >= 1.5 * std::numbers::pi) {
+                _angleInRads = _angleInRads - 2.0 * std::numbers::pi;
+            } else if (_angleInRads >= std::numbers::pi / 2.0) {
+                _angleInRads = std::numbers::pi - _angleInRads;
+            } else if (_angleInRads <= -1.5 * std::numbers::pi) {
+                _angleInRads += 2.0 * std::numbers::pi;
+            } else if (_angleInRads <= -std::numbers::pi / 2.0) {
+                _angleInRads = -(std::numbers::pi + _angleInRads);
+            }
+        }
+
+        return *this;
+    }
+
+    MccAngle& normalize()
+    {
+        return normalize<NORM_KIND_0_360>();
+    }
+
+
+    // template <typename T>
+    // operator T() const
+    //     requires std::is_arithmetic_v<T>
+    // {
+    //     return _angleInRads;
+    // }
+
+    constexpr operator double() const
+    {
+        return _angleInRads;
+    }
+
+
+    template <typename T>
+    constexpr T degrees() const
+    {
+        return _angleInRads * 180.0 / std::numbers::pi;
+    }
+
+    constexpr double degrees() const
+    {
+        return degrees<double>();
+    }
+
+
+    template <typename T>
+    T arcmins() const
+    {
+        return _angleInRads * 10800.0 / std::numbers::pi;
+    }
+
+    double arcmins() const
+    {
+        return arcmins<double>();
+    }
+
+
+    template <typename T>
+    T arcsecs() const
+    {
+        return _angleInRads * 648000.0 / std::numbers::pi;
+    }
+
+    double arcsecs() const
+    {
+        return arcsecs<double>();
+    }
+
+    template <typename T>
+    T hours() const
+    {
+        return _angleInRads * 12.0 / std::numbers::pi;
+    }
+
+    double hours() const
+    {
+        return hours<double>();
+    }
+
+    template <typename T>
+    T minutes() const
+    {
+        return _angleInRads * 720.0 / std::numbers::pi;
+    }
+
+    double minutes() const
+    {
+        return minutes<double>();
+    }
+
+    template <typename T>
+    T seconds() const
+    {
+        return _angleInRads * 43200.0 / std::numbers::pi;
+    }
+
+    double seconds() const
+    {
+        return seconds<double>();
+    }
+
+
+    template <traits::mcc_output_char_range T>
+    T sexagesimal(bool hms = false, int prec = 2) const
+    {
+        return utils::rad2sxg(_angleInRads, hms, prec >= 0 ? prec : _precision);
+    }
+
+    std::string sexagesimal(bool hms = false, int prec = 2) const
+    {
+        return sexagesimal<std::string>(hms, prec);
+    }
+
+
+    // arithmetics
+
+    template <typename SelfT, std::convertible_to<MccAngle> T>
+    SelfT& operator+=(this SelfT& self, const T& v)
+    {
+        if constexpr (std::derived_from<T, MccAngle>) {
+            static_assert(std::derived_from<SelfT, T>, "INCOMPATIBLE TYPES!");
+
+            self._angleInRads += v._angleInRads;
+        } else if constexpr (std::is_arithmetic_v<T>) {
+            self._angleInRads += v;
+        } else {
+            self._angleInRads += MccAngle(v)._angleInRads;
+        }
+
+        return self;
+    }
+
+    template <typename SelfT, std::convertible_to<MccAngle> T>
+    SelfT& operator-=(this SelfT& self, const T& v)
+    {
+        if constexpr (std::derived_from<T, MccAngle>) {
+            static_assert(std::derived_from<SelfT, T>, "INCOMPATIBLE TYPES!");
+
+            self._angleInRads -= v._angleInRads;
+        } else if constexpr (std::is_arithmetic_v<T>) {
+            self._angleInRads -= v;
+        } else {
+            self._angleInRads -= MccAngle(v)._angleInRads;
+        }
+
+        return self;
+    }
+
+    template <typename SelfT, typename T>
+    SelfT& operator*=(this SelfT& self, const T& v)
+        requires std::is_arithmetic_v<T>
+    {
+        self._angleInRads *= v;
+
+        return self;
+    }
+
+    template <typename SelfT, typename T>
+    SelfT& operator/=(this SelfT& self, const T& v)
+        requires std::is_arithmetic_v<T>
+    {
+        self._angleInRads /= v;
+
+        return self;
+    }
+
+
+    // unary '-' and '+'
+    template <typename SelfT>
+    SelfT operator-(this SelfT& self)
+    {
+        SelfT res = -self._angleInRads;
+
+        return res;
+    }
+
+    template <typename SelfT>
+    SelfT operator+(this SelfT& self)
+    {
+        return self;
+    }
+};
+
+
+// binary arithmetic operations
+
+template <std::convertible_to<MccAngle> T1, std::convertible_to<MccAngle> T2>
+static auto operator+(const T1& v1, const T2& v2)
+{
+    static_assert(std::convertible_to<T1, T2> || std::convertible_to<T2, T1>, "INCOMPATIBLE TYPES!");
+
+    using res_t = std::conditional_t<std::convertible_to<T1, T2> && std::derived_from<T1, MccAngle>, T1, T2>;
+
+    return res_t{(double)v1 + (double)v2};
+}
+
+template <std::convertible_to<MccAngle> T1, std::convertible_to<MccAngle> T2>
+static auto operator-(const T1& v1, const T2& v2)
+{
+    static_assert(std::convertible_to<T1, T2> || std::convertible_to<T2, T1>, "INCOMPATIBLE TYPES!");
+
+    using res_t = std::conditional_t<std::convertible_to<T1, T2> && std::derived_from<T1, MccAngle>, T1, T2>;
+
+    return res_t{(double)v1 - (double)v2};
+}
+
+
+template <std::convertible_to<MccAngle> T1, std::convertible_to<MccAngle> T2>
+static auto operator*(const T1& v1, const T2& v2)
+{
+    if constexpr (std::is_arithmetic_v<T1>) {
+        return v2 *= v1;
+    } else if constexpr (std::is_arithmetic_v<T2>) {
+        return v1 *= v2;
+    } else {
+        using res_t = std::conditional_t<std::convertible_to<T1, T2> && std::derived_from<T1, MccAngle>, T1, T2>;
+        return res_t{(double)v1 * (double)v2};
+        // static_assert(false, "INCOMPATIBLE TYPES!");
+    }
+}
+
+template <std::convertible_to<MccAngle> T1, typename T2>
+static auto operator/(const T1& v1, const T2& v2)
+    requires std::is_arithmetic_v<T2>
+{
+    return v1 /= v2;
+}
+
+
+/*  */
+
+class MccAngleRA_ICRS : public MccAngle
+{
+    using MccAngle::MccAngle;
+};
+
+class MccAngleDEC_ICRS : public MccAngle
+{
+    using MccAngle::MccAngle;
+};
+
+class MccAngleRA_APP : public MccAngle
+{
+    using MccAngle::MccAngle;
+};
+
+class MccAngleDEC_APP : public MccAngle
+{
+    using MccAngle::MccAngle;
+};
+
+class MccAngleHA : public MccAngle
+{
+    using MccAngle::MccAngle;
+};
+
+class MccAngleAZ : public MccAngle
+{
+    using MccAngle::MccAngle;
+};
+
+class MccAngleZD : public MccAngle
+{
+public:
+    using MccAngle::MccAngle;
+};
+
+class MccAngleALT : public MccAngle
+{
+public:
+    using MccAngle::MccAngle;
+};
+
+
+class MccAngleX : public MccAngle  // some co-longitude coordinate
+{
+    using MccAngle::MccAngle;
+};
+
+class MccAngleY : public MccAngle  // some co-latitude coordinate
+{
+    using MccAngle::MccAngle;
+};
+
+
+
+class MccAngleLAT : public MccAngle
+{
+    using MccAngle::MccAngle;
+};
+
+class MccAngleLON : public MccAngle
+{
+    using MccAngle::MccAngle;
+};
+
+
+enum class MccCoordKind : size_t {
+    COORDS_KIND_GENERIC = traits::mcc_type_hash<MccAngle>,
+    COORDS_KIND_RA_ICRS = traits::mcc_type_hash<MccAngleRA_ICRS>,
+    COORDS_KIND_DEC_ICRS = traits::mcc_type_hash<MccAngleDEC_ICRS>,
+    COORDS_KIND_RA_APP = traits::mcc_type_hash<MccAngleRA_APP>,
+    COORDS_KIND_DEC_APP = traits::mcc_type_hash<MccAngleDEC_APP>,
+    COORDS_KIND_HA = traits::mcc_type_hash<MccAngleHA>,
+    COORDS_KIND_AZ = traits::mcc_type_hash<MccAngleAZ>,
+    COORDS_KIND_ZD = traits::mcc_type_hash<MccAngleZD>,
+    COORDS_KIND_ALT = traits::mcc_type_hash<MccAngleALT>,
+    COORDS_KIND_X = traits::mcc_type_hash<MccAngleX>,
+    COORDS_KIND_Y = traits::mcc_type_hash<MccAngleY>,
+    COORDS_KIND_LAT = traits::mcc_type_hash<MccAngleLAT>,
+    COORDS_KIND_LON = traits::mcc_type_hash<MccAngleLON>
+};
+
+enum class MccCoordPairKind : size_t {
+    COORDS_KIND_GENERIC = traits::mcc_type_pair_hash<MccAngle, MccAngle>(),
+    COORDS_KIND_RADEC_ICRS = traits::mcc_type_pair_hash<MccAngleRA_ICRS, MccAngleDEC_ICRS>(),
+    COORDS_KIND_RADEC_APP = traits::mcc_type_pair_hash<MccAngleRA_APP, MccAngleDEC_APP>(),
+    COORDS_KIND_HADEC_APP = traits::mcc_type_pair_hash<MccAngleHA, MccAngleDEC_APP>(),
+    COORDS_KIND_AZZD = traits::mcc_type_pair_hash<MccAngleAZ, MccAngleZD>(),
+    COORDS_KIND_AZALT = traits::mcc_type_pair_hash<MccAngleAZ, MccAngleALT>(),
+    COORDS_KIND_XY = traits::mcc_type_pair_hash<MccAngleX, MccAngleY>(),
+    COORDS_KIND_LATLON = traits::mcc_type_pair_hash<MccAngleLAT, MccAngleLON>()
+};
+
+
+template <MccCoordPairKind KIND>
+static constexpr std::string_view MccCoordPairKindStr =
+    KIND == MccCoordPairKind::COORDS_KIND_RADEC_ICRS  ? "RADEC-IRCS"
+    : KIND == MccCoordPairKind::COORDS_KIND_RADEC_APP ? "RADEC-APP"
+    : KIND == MccCoordPairKind::COORDS_KIND_HADEC_APP ? "HADEC-APP"
+    : KIND == MccCoordPairKind::COORDS_KIND_AZALT     ? "Azimuth-Altitude"
+    : KIND == MccCoordPairKind::COORDS_KIND_AZZD      ? "Azimuth-Zendist"
+    : KIND == MccCoordPairKind::COORDS_KIND_XY        ? "X-Y"
+    : KIND == MccCoordPairKind::COORDS_KIND_LATLON    ? "Latitude-Longitude"
+                                                      : "UNKNOWN";
+
+
+}  // namespace mcc
diff --git a/mcc/mcc_ccte_erfa.h b/mcc/mcc_ccte_erfa.h
index 619b0f3..abbcdd8 100644
--- a/mcc/mcc_ccte_erfa.h
+++ b/mcc/mcc_ccte_erfa.h
@@ -10,6 +10,7 @@
 #include <mutex>
 
 
+#include "mcc_angle.h"
 #include "mcc_ccte_iers.h"
 #include "mcc_defaults.h"
 
@@ -116,6 +117,8 @@ inline std::error_code make_error_code(MccCCTE_ERFAErrorCode ec)
 
 class MccCCTE_ERFA
 {
+    static constexpr double PI_2 = std::numbers::pi / 2.0;
+
 public:
     static constexpr double DEFAULT_WAVELENGTH = 0.55;  // default observed wavelength in mkm
 
@@ -160,6 +163,14 @@ public:
 
     MccCCTE_ERFA() : _stateMutex(new std::mutex) {}
 
+    MccCCTE_ERFA(engine_state_t state) : _currentState(std::move(state)), _stateMutex(new std::mutex) {}
+
+    MccCCTE_ERFA(const MccCCTE_ERFA&) = delete;
+    MccCCTE_ERFA& operator=(const MccCCTE_ERFA&) = delete;
+
+    MccCCTE_ERFA(MccCCTE_ERFA&&) = default;
+    MccCCTE_ERFA& operator=(MccCCTE_ERFA&&) = default;
+
     virtual ~MccCCTE_ERFA() = default;
 
     // engine state related methods
@@ -344,60 +355,12 @@ public:
                 from_pt.pair_kind == MccCoordPairKind::COORDS_KIND_RADEC_APP ||
                 from_pt.pair_kind == MccCoordPairKind::COORDS_KIND_HADEC_APP) {
                 //
-                ret = timepointToJulday(from_pt.time_point, &jd);
-                if (ret) {
-                    return ret;
-                }
-
-                std::lock_guard lock{*_stateMutex};
-
-                auto dut1 = _currentState._bulletinA.DUT1(jd.mjd);
-
-                if (!dut1.has_value()) {
-                    return MccCCTE_ERFAErrorCode::ERROR_BULLETINA_OUT_OF_RANGE;
-                }
-
-                auto pol_pos = _currentState._bulletinA.polarCoords(jd.mjd);
-                if (!pol_pos.has_value()) {
-                    return MccCCTE_ERFAErrorCode::ERROR_BULLETINA_OUT_OF_RANGE;
-                }
-                const auto arcsec2rad = std::numbers::pi / 180 / 3600;
-                pol_pos->x *= arcsec2rad;
-                pol_pos->y *= arcsec2rad;
-
-                std::string type;
-                switch (from_pt.pair_kind) {
-                    case mcc::MccCoordPairKind::COORDS_KIND_AZZD:
-                        type = "A";
-                        break;
-                    case mcc::MccCoordPairKind::COORDS_KIND_AZALT:
-                        from_pt.Y = std::numbers::pi / 2.0 - from_pt.Y;  // altitude to zenithal distance
-                        type = "A";
-                        break;
-                    case mcc::MccCoordPairKind::COORDS_KIND_HADEC_APP:
-                        type = "H";
-                        break;
-                    case mcc::MccCoordPairKind::COORDS_KIND_RADEC_APP:
-                        type = "R";
-                        break;
-                    default:
-                        return MccCCTE_ERFAErrorCode::ERROR_UNSUPPORTED_COORD_PAIR;
-                }
-
-                int err = eraAtoc13(type.c_str(), from_pt.X, from_pt.Y, jd.MJD0, jd.mjd, dut1->count(),
-                                    _currentState.lon, _currentState.lat, _currentState.elev, pol_pos->x, pol_pos->y,
-                                    _currentState.meteo.pressure, _currentState.meteo.temperature,
-                                    _currentState.meteo.humidity, _currentState.wavelength, &to_pt->X, &to_pt->Y);
-
-                if (err == 1) {
-                    return MccCCTE_ERFAErrorCode::ERROR_DUBIOUS_YEAR;
-                } else if (err == -1) {
-                    return MccCCTE_ERFAErrorCode::ERROR_UNACCEPTABLE_DATE;
-                }
             } else {
                 ret = MccCCTE_ERFAErrorCode::ERROR_UNSUPPORTED_COORD_PAIR;
             }
 
+            ret = obs2icrs(from_pt, to_pt);
+
             return ret;
         }
 
@@ -409,53 +372,24 @@ public:
                 to_pt->pair_kind == MccCoordPairKind::COORDS_KIND_RADEC_APP ||
                 to_pt->pair_kind == MccCoordPairKind::COORDS_KIND_HADEC_APP) {
                 //
-                ret = timepointToJulday(to_pt->time_point, &jd);
-                if (ret) {
-                    return ret;
-                }
+                MccEqtHrzCoords eqhrz;
 
-                std::lock_guard lock{*_stateMutex};
+                ret = icrs2obs(from_pt, &eqhrz);
 
-                auto dut1 = _currentState._bulletinA.DUT1(jd.mjd);
-
-                if (!dut1.has_value()) {
-                    return MccCCTE_ERFAErrorCode::ERROR_BULLETINA_OUT_OF_RANGE;
-                }
-
-                auto pol_pos = _currentState._bulletinA.polarCoords(jd.mjd);
-                if (!pol_pos.has_value()) {
-                    return MccCCTE_ERFAErrorCode::ERROR_BULLETINA_OUT_OF_RANGE;
-                }
-                const auto arcsec2rad = std::numbers::pi / 180 / 3600;
-                pol_pos->x *= arcsec2rad;
-                pol_pos->y *= arcsec2rad;
-
-                double oaz, ozd, oha, odec, ora, eo_;
-
-                int err = eraAtco13(from_pt.X, from_pt.Y, 0.0, 0.0, 0.0, 0.0, jd.MJD0, jd.mjd, dut1->count(),
-                                    _currentState.lon, _currentState.lat, _currentState.elev, pol_pos->x, pol_pos->y,
-                                    _currentState.meteo.pressure, _currentState.meteo.temperature,
-                                    _currentState.meteo.humidity, _currentState.wavelength, &oaz, &ozd, &oha, &odec,
-                                    &ora, &eo_);
-
-                if (err == 1) {
-                    return MccCCTE_ERFAErrorCode::ERROR_DUBIOUS_YEAR;
-                } else if (err == -1) {
-                    return MccCCTE_ERFAErrorCode::ERROR_UNACCEPTABLE_DATE;
-                }
-
-                if (to_pt->pair_kind == MccCoordPairKind::COORDS_KIND_AZALT) {
-                    to_pt->X = oaz;
-                    to_pt->Y = std::numbers::pi / 2.0 - ozd;
-                } else if (to_pt->pair_kind == MccCoordPairKind::COORDS_KIND_AZZD) {
-                    to_pt->X = oaz;
-                    to_pt->Y = ozd;
-                } else if (to_pt->pair_kind == MccCoordPairKind::COORDS_KIND_RADEC_APP) {
-                    to_pt->X = ora;
-                    to_pt->Y = odec;
-                } else if (to_pt->pair_kind == MccCoordPairKind::COORDS_KIND_HADEC_APP) {
-                    to_pt->X = oha;
-                    to_pt->Y = odec;
+                if (!ret) {
+                    if (to_pt->pair_kind == MccCoordPairKind::COORDS_KIND_AZALT) {
+                        to_pt->X = eqhrz.AZ;
+                        to_pt->Y = eqhrz.ALT;
+                    } else if (to_pt->pair_kind == MccCoordPairKind::COORDS_KIND_AZZD) {
+                        to_pt->X = eqhrz.AZ;
+                        to_pt->Y = eqhrz.ZD;
+                    } else if (to_pt->pair_kind == MccCoordPairKind::COORDS_KIND_RADEC_APP) {
+                        to_pt->X = eqhrz.RA_APP;
+                        to_pt->Y = eqhrz.DEC_APP;
+                    } else if (to_pt->pair_kind == MccCoordPairKind::COORDS_KIND_HADEC_APP) {
+                        to_pt->X = eqhrz.HA;
+                        to_pt->Y = eqhrz.DEC_APP;
+                    }
                 }
             } else {
                 ret = MccCCTE_ERFAErrorCode::ERROR_UNSUPPORTED_COORD_PAIR;
@@ -463,6 +397,202 @@ public:
 
             return ret;
         }
+
+
+        // from apparent to apparent
+        if (from_pt.time_point != to_pt->time_point) {  // first, convert 'from' coordinates to ICRS
+            MccCelestialPoint pt{.time_point = to_pt->time_point,
+                                 .pair_kind = MccCoordPairKind::COORDS_KIND_RADEC_ICRS};
+            ret = obs2icrs(from_pt, &pt);
+
+            if (!ret) {  // from ICRS to required
+                return transformCoordinates(pt, to_pt);
+            }
+        } else {  // the same time points
+            double eo, lst, ha, dec, az, alt;
+
+            auto lst_eo = [&]() {
+                ret = eqOrigins(from_pt.time_point, &eo);
+                if (!ret) {
+                    ret = timepointToAppSideral(from_pt.time_point, &lst, true);
+                }
+            };
+
+            if (from_pt.pair_kind == MccCoordPairKind::COORDS_KIND_RADEC_APP) {
+                // first, compute HA from CIO-based RA!!!
+                lst_eo();
+                if (!ret) {
+                    ha = lst - from_pt.X + eo;
+                } else {
+                    return ret;
+                }
+
+                if (to_pt->pair_kind == MccCoordPairKind::COORDS_KIND_AZZD) {
+                    eraHd2ae(ha, from_pt.Y, _currentState.lat, &az, &alt);
+                    to_pt->X = az;
+                    to_pt->Y = PI_2 - alt;
+                } else if (to_pt->pair_kind == MccCoordPairKind::COORDS_KIND_AZALT) {
+                    eraHd2ae(ha, from_pt.Y, _currentState.lat, &az, &alt);
+                    to_pt->X = az;
+                    to_pt->Y = alt;
+                } else if (to_pt->pair_kind == MccCoordPairKind::COORDS_KIND_HADEC_APP) {
+                    to_pt->X = ha;
+                    to_pt->Y = from_pt.Y;
+                } else {
+                    ret = MccCCTE_ERFAErrorCode::ERROR_UNSUPPORTED_COORD_PAIR;
+                }
+            } else if (from_pt.pair_kind == MccCoordPairKind::COORDS_KIND_HADEC_APP) {
+                if (to_pt->pair_kind == MccCoordPairKind::COORDS_KIND_AZZD) {
+                    eraHd2ae(ha, from_pt.Y, _currentState.lat, &az, &alt);
+                    to_pt->X = az;
+                    to_pt->Y = PI_2 - alt;
+                } else if (to_pt->pair_kind == MccCoordPairKind::COORDS_KIND_AZALT) {
+                    eraHd2ae(ha, from_pt.Y, _currentState.lat, &az, &alt);
+                    to_pt->X = az;
+                    to_pt->Y = alt;
+                } else if (to_pt->pair_kind == MccCoordPairKind::COORDS_KIND_RADEC_APP) {
+                    lst_eo();
+                    if (!ret) {
+                        to_pt->X = lst - from_pt.X + eo;
+                        to_pt->Y = from_pt.Y;
+                    } else {
+                        return ret;
+                    }
+                } else {
+                    ret = MccCCTE_ERFAErrorCode::ERROR_UNSUPPORTED_COORD_PAIR;
+                }
+
+            } else if (from_pt.pair_kind == MccCoordPairKind::COORDS_KIND_AZZD) {
+                from_pt.Y = PI_2 - from_pt.Y;
+                from_pt.pair_kind = MccCoordPairKind::COORDS_KIND_AZALT;
+
+                ret = transformCoordinates(std::move(from_pt), to_pt);
+            } else if (from_pt.pair_kind == MccCoordPairKind::COORDS_KIND_AZALT) {
+                if (to_pt->pair_kind == MccCoordPairKind::COORDS_KIND_HADEC_APP) {
+                    eraAe2hd(from_pt.X, from_pt.Y, _currentState.lat, &ha, &dec);
+                    to_pt->X = ha;
+                    to_pt->Y = dec;
+                } else if (to_pt->pair_kind == MccCoordPairKind::COORDS_KIND_AZZD) {
+                    to_pt->X = from_pt.X;
+                    to_pt->Y = PI_2 - from_pt.Y;
+                } else if (to_pt->pair_kind == MccCoordPairKind::COORDS_KIND_RADEC_APP) {
+                    eraAe2hd(from_pt.X, from_pt.Y, _currentState.lat, &ha, &dec);
+                    lst_eo();
+                    if (!ret) {
+                        to_pt->X = lst - ha + eo;
+                        to_pt->Y = dec;
+                    }
+                } else {
+                    ret = MccCCTE_ERFAErrorCode::ERROR_UNSUPPORTED_COORD_PAIR;
+                }
+
+            } else {
+                ret = MccCCTE_ERFAErrorCode::ERROR_UNSUPPORTED_COORD_PAIR;
+            }
+        }
+
+        return ret;
+    }
+
+
+    error_t transformCoordinates(mcc_celestial_point_c auto from_pt, mcc_eqt_hrz_coord_c auto* to_pt)
+    {
+        error_t ret = MccCCTE_ERFAErrorCode::ERROR_OK;
+
+        MccJulianDay jd;
+
+        if (to_pt == nullptr) {
+            return ret;
+        }
+
+        using tp_pt_t = std::remove_cvref_t<decltype(*to_pt)>;
+        MccGenericCelestialPoint<typename tp_pt_t::coord_t> cpt;
+        cpt.time_point = from_pt.time_point;
+
+        // the main scenario: from ICRS to apparent
+        if (from_pt.pair_kind == MccCoordPairKind::COORDS_KIND_RADEC_ICRS) {
+            return icrs2obs(from_pt, to_pt);
+        }
+
+        // from apparent: copy corresponded coordinates and compute other ones
+        if (from_pt.pair_kind == MccCoordPairKind::COORDS_KIND_RADEC_APP) {
+            to_pt->RA_APP = from_pt.X;
+            to_pt->DEC_APP = from_pt.Y;
+
+            cpt.pair_kind = MccCoordPairKind::COORDS_KIND_HADEC_APP;
+
+            ret = transformCoordinates(from_pt, &cpt);
+            if (!ret) {
+                to_pt->HA = cpt.X;
+
+                auto cpt1 = cpt;
+                cpt1.pair_kind = MccCoordPairKind::COORDS_KIND_AZALT;
+
+                ret = transformCoordinates(cpt, &cpt1);
+                if (!ret) {
+                    to_pt->AZ = cpt1.X;
+                    to_pt->ALT = cpt1.Y;
+                    to_pt->ZD = PI_2 - cpt1.Y;
+                }
+            }
+        } else if (from_pt.pair_kind == MccCoordPairKind::COORDS_KIND_HADEC_APP) {
+            to_pt->HA = from_pt.X;
+            to_pt->DEC_APP = from_pt.Y;
+
+            cpt.pair_kind = MccCoordPairKind::COORDS_KIND_RADEC_APP;
+            ret = transformCoordinates(from_pt, &cpt);
+            if (!ret) {
+                to_pt->RA_APP = cpt.X;
+
+                cpt.pair_kind = MccCoordPairKind::COORDS_KIND_AZALT;
+                ret = transformCoordinates(from_pt, &cpt);
+                if (!ret) {
+                    to_pt->AZ = cpt.X;
+                    to_pt->ALT = cpt.Y;
+                    to_pt->ZD = PI_2 - cpt.Y;
+                }
+            }
+        } else if (from_pt.pair_kind == MccCoordPairKind::COORDS_KIND_AZZD) {
+            to_pt->AZ = from_pt.X;
+            to_pt->ZD = from_pt.Y;
+            to_pt->ALT = PI_2 - from_pt.Y;
+
+            cpt.pair_kind = MccCoordPairKind::COORDS_KIND_HADEC_APP;
+            ret = transformCoordinates(from_pt, &cpt);
+            if (!ret) {
+                to_pt->HA = cpt.X;
+                to_pt->DEC_APP = cpt.Y;
+
+                auto cpt1 = cpt;
+                cpt1.pair_kind = MccCoordPairKind::COORDS_KIND_RADEC_APP;
+                ret = transformCoordinates(cpt, &cpt1);
+                if (!ret) {
+                    to_pt->RA_APP = cpt1.X;
+                }
+            }
+        } else if (from_pt.pair_kind == MccCoordPairKind::COORDS_KIND_AZALT) {
+            to_pt->AZ = from_pt.X;
+            to_pt->ALT = from_pt.Y;
+            to_pt->ZD = PI_2 - from_pt.Y;
+
+            cpt.pair_kind = MccCoordPairKind::COORDS_KIND_HADEC_APP;
+            ret = transformCoordinates(from_pt, &cpt);
+            if (!ret) {
+                to_pt->HA = cpt.X;
+                to_pt->DEC_APP = cpt.Y;
+
+                auto cpt1 = cpt;
+                cpt1.pair_kind = MccCoordPairKind::COORDS_KIND_RADEC_APP;
+                ret = transformCoordinates(cpt, &cpt1);
+                if (!ret) {
+                    to_pt->RA_APP = cpt1.X;
+                }
+            }
+        } else {
+            ret = MccCCTE_ERFAErrorCode::ERROR_UNSUPPORTED_COORD_PAIR;
+        }
+
+        return ret;
     }
 
 
@@ -536,6 +666,154 @@ protected:
     engine_state_t _currentState{};
 
     std::unique_ptr<std::mutex> _stateMutex;
+
+    error_t icrs2obs(mcc_celestial_point_c auto const& pt, mcc_eqt_hrz_coord_c auto* result)
+    {
+        if (result == nullptr) {
+            return MccCCTE_ERFAErrorCode::ERROR_OK;
+        }
+
+        MccJulianDay jd;
+
+        auto ret = timepointToJulday(result->time_point, &jd);
+        if (ret) {
+            return ret;
+        }
+
+        std::lock_guard lock{*_stateMutex};
+
+        auto dut1 = _currentState._bulletinA.DUT1(jd.mjd);
+
+        if (!dut1.has_value()) {
+            return MccCCTE_ERFAErrorCode::ERROR_BULLETINA_OUT_OF_RANGE;
+        }
+
+        auto pol_pos = _currentState._bulletinA.polarCoords(jd.mjd);
+        if (!pol_pos.has_value()) {
+            return MccCCTE_ERFAErrorCode::ERROR_BULLETINA_OUT_OF_RANGE;
+        }
+
+        // const auto arcsec2rad = std::numbers::pi / 180 / 3600;
+        const auto arcsec2rad = 1.0_arcsecs;
+        pol_pos->x *= arcsec2rad;
+        pol_pos->y *= arcsec2rad;
+
+        double az, zd, ha, ra, dec, eo;
+
+        int err = eraAtco13(pt.X, pt.Y, 0.0, 0.0, 0.0, 0.0, jd.MJD0, jd.mjd, dut1->count(), _currentState.lon,
+                            _currentState.lat, _currentState.elev, pol_pos->x, pol_pos->y, _currentState.meteo.pressure,
+                            _currentState.meteo.temperature, _currentState.meteo.humidity, _currentState.wavelength,
+                            &az, &zd, &ha, &dec, &ra, &eo);
+
+        if (err == 1) {
+            ret = MccCCTE_ERFAErrorCode::ERROR_DUBIOUS_YEAR;
+        } else if (err == -1) {
+            ret = MccCCTE_ERFAErrorCode::ERROR_UNACCEPTABLE_DATE;
+        }
+
+        result->AZ = az;
+        result->ZD = zd;
+        result->HA = ha;
+        result->RA_APP = ra;
+        result->DEC_APP = dec;
+        result->ALT = std::numbers::pi / 2.0 - zd;
+
+        return ret;
+    }
+
+
+    error_t obs2icrs(mcc_celestial_point_c auto const& from_pt, mcc_celestial_point_c auto* to_pt)
+    {
+        if (to_pt == nullptr) {
+            return MccCCTE_ERFAErrorCode::ERROR_OK;
+        }
+
+        MccJulianDay jd;
+
+        auto ret = timepointToJulday(from_pt.time_point, &jd);
+        if (ret) {
+            return ret;
+        }
+
+        std::lock_guard lock{*_stateMutex};
+
+        auto dut1 = _currentState._bulletinA.DUT1(jd.mjd);
+
+        if (!dut1.has_value()) {
+            return MccCCTE_ERFAErrorCode::ERROR_BULLETINA_OUT_OF_RANGE;
+        }
+
+        auto pol_pos = _currentState._bulletinA.polarCoords(jd.mjd);
+        if (!pol_pos.has_value()) {
+            return MccCCTE_ERFAErrorCode::ERROR_BULLETINA_OUT_OF_RANGE;
+        }
+
+        // const auto arcsec2rad = std::numbers::pi / 180 / 3600;
+        const auto arcsec2rad = 1.0_arcsecs;
+        pol_pos->x *= arcsec2rad;
+        pol_pos->y *= arcsec2rad;
+
+        std::string type;
+        switch (from_pt.pair_kind) {
+            case mcc::MccCoordPairKind::COORDS_KIND_AZZD:
+                type = "A";
+                break;
+            case mcc::MccCoordPairKind::COORDS_KIND_AZALT:
+                from_pt.Y = std::numbers::pi / 2.0 - from_pt.Y;  // altitude to zenithal distance
+                type = "A";
+                break;
+            case mcc::MccCoordPairKind::COORDS_KIND_HADEC_APP:
+                type = "H";
+                break;
+            case mcc::MccCoordPairKind::COORDS_KIND_RADEC_APP:
+                type = "R";
+                break;
+            default:
+                return MccCCTE_ERFAErrorCode::ERROR_UNSUPPORTED_COORD_PAIR;
+        }
+
+        int err = eraAtoc13(type.c_str(), from_pt.X, from_pt.Y, jd.MJD0, jd.mjd, dut1->count(), _currentState.lon,
+                            _currentState.lat, _currentState.elev, pol_pos->x, pol_pos->y, _currentState.meteo.pressure,
+                            _currentState.meteo.temperature, _currentState.meteo.humidity, _currentState.wavelength,
+                            &to_pt->X, &to_pt->Y);
+
+        if (err == 1) {
+            return MccCCTE_ERFAErrorCode::ERROR_DUBIOUS_YEAR;
+        } else if (err == -1) {
+            return MccCCTE_ERFAErrorCode::ERROR_UNACCEPTABLE_DATE;
+        }
+    }
+
+    error_t eqOrigins(mcc_time_point_c auto const& tp, double* eo)
+    {
+        if (eo == nullptr) {
+            return MccCCTE_ERFAErrorCode::ERROR_OK;
+        }
+
+        MccJulianDay jd, tt;
+        auto ret = timepointToJulday(tp, &jd);
+        if (ret) {
+            return ret;
+        }
+
+        std::lock_guard lock{*_stateMutex};
+
+        using real_days_t = std::chrono::duration<double, std::ratio<86400>>;
+
+        auto tai_utc = _currentState._leapSeconds[jd.mjd];
+        if (tai_utc.has_value()) {
+            tt.mjd = jd.mjd + std::chrono::duration_cast<real_days_t>(tai_utc.value()).count();
+
+            auto tt_tai = _currentState._bulletinA.TT_TAI();
+            tt.mjd = jd.mjd + std::chrono::duration_cast<real_days_t>(tt_tai).count();
+
+            *eo = eraEo06a(tt.MJD0, tt.mjd);
+        } else {
+            ret = MccCCTE_ERFAErrorCode::ERROR_LEAPSECONDS_OUT_OF_RANGE;
+        }
+
+        return ret;
+    }
 };
 
 }  // namespace mcc::ccte::erfa
diff --git a/mcc/mcc_generics.h b/mcc/mcc_generics.h
index a473c5b..3c8fc39 100644
--- a/mcc/mcc_generics.h
+++ b/mcc/mcc_generics.h
@@ -11,7 +11,8 @@
 #include <concepts>
 
 
-#include "mcc_traits.h"
+// #include "mcc_traits.h"
+#include "mcc_angle.h"
 
 namespace mcc
 {
@@ -20,16 +21,16 @@ namespace mcc
 // mount construction type (only the most common ones)
 enum class MccMountType : uint8_t { GERMAN_TYPE, FORK_TYPE, CROSSAXIS_TYPE, ALTAZ_TYPE };
 
-enum MccCoordPairKind : size_t {
-    COORDS_KIND_GENERIC,
-    COORDS_KIND_RADEC_ICRS,
-    COORDS_KIND_RADEC_APP,
-    COORDS_KIND_HADEC_APP,
-    COORDS_KIND_AZZD,
-    COORDS_KIND_AZALT,
-    COORDS_KIND_XY,
-    COORDS_KIND_LATLON
-};
+// enum MccCoordPairKind : size_t {
+//     COORDS_KIND_GENERIC,
+//     COORDS_KIND_RADEC_ICRS,
+//     COORDS_KIND_RADEC_APP,
+//     COORDS_KIND_HADEC_APP,
+//     COORDS_KIND_AZZD,
+//     COORDS_KIND_AZALT,
+//     COORDS_KIND_XY,
+//     COORDS_KIND_LATLON
+// };
 
 
 /*                          FLOATING-POINT LIKE CLASS CONCEPT                           */
@@ -165,14 +166,13 @@ protected:
 
 
 template <typename T>
-concept mcc_ast_engine_c =
-    std::derived_from<T, mcc_CCTE_interface_t<typename T::error_t>> && requires(const T t_const, T t) {
-        { t_const.name() } -> std::formattable<char>;
+concept mcc_ccte_c = std::derived_from<T, mcc_CCTE_interface_t<typename T::error_t>> && requires(const T t_const, T t) {
+    { t_const.name() } -> std::formattable<char>;
 
-        requires mcc_refract_model_c<typename T::refract_model_t>;
+    requires mcc_refract_model_c<typename T::refract_model_t>;
 
-        { t.refractionModel(std::declval<typename T::refract_model_t*>()) } -> std::same_as<typename T::error_t>;
-    };
+    { t.refractionModel(std::declval<typename T::refract_model_t*>()) } -> std::same_as<typename T::error_t>;
+};
 
 
 
@@ -303,7 +303,8 @@ struct mcc_pzone_interface_t {
 
     template <std::derived_from<mcc_pzone_interface_t> SelfT, typename InputT>
     RetT inPZone(this SelfT&& self, InputT coords, bool* result)
-        requires(mcc_eqt_hrz_coord_c<InputT> || mcc_celestial_point_c<InputT>)
+        requires(mcc_eqt_hrz_coord_c<InputT> || mcc_celestial_point_c<InputT>) &&
+                requires { self.inPZone(coords, result); }
     {
         return std::forward<SelfT>(self).InPZone(std::move(coords), result);
     }
@@ -311,14 +312,16 @@ struct mcc_pzone_interface_t {
 
     template <std::derived_from<mcc_pzone_interface_t> SelfT, typename InputT>
     RetT timeToPZone(this SelfT&& self, InputT coords, traits::mcc_time_duration_c auto* res_time)
-        requires(mcc_eqt_hrz_coord_c<InputT> || mcc_celestial_point_c<InputT>)
+        requires(mcc_eqt_hrz_coord_c<InputT> || mcc_celestial_point_c<InputT>) &&
+                requires { self.timeToPZone(coords, res_time); }
     {
         return std::forward<SelfT>(self).timeToPZone(std::move(coords), res_time);
     }
 
     template <std::derived_from<mcc_pzone_interface_t> SelfT, typename InputT>
     RetT timeFromPZone(this SelfT&& self, InputT coords, traits::mcc_time_duration_c auto* res_time)
-        requires(mcc_eqt_hrz_coord_c<InputT> || mcc_celestial_point_c<InputT>)
+        requires(mcc_eqt_hrz_coord_c<InputT> || mcc_celestial_point_c<InputT>) &&
+                requires { self.timeFromPZone(coords, res_time); }
     {
         return std::forward<SelfT>(self).timeFromPZone(std::move(coords), res_time);
     }
diff --git a/mcc/mcc_pzone.h b/mcc/mcc_pzone.h
new file mode 100644
index 0000000..dd9af90
--- /dev/null
+++ b/mcc/mcc_pzone.h
@@ -0,0 +1,78 @@
+#pragma once
+
+/*                          MOUNT CONTROL COMPONENTS LIBRARY                            */
+
+
+/*                          IMPLEMENTATION OF SOME SIMPLE PROHIBITED ZONES              */
+
+#include "mcc_generics.h"
+
+namespace mcc
+{
+
+static constexpr double mcc_sideral_to_UT1_ratio = 1.002737909350795;  // sideral/UT1
+
+
+/*                          MINIMAL OR MAXIMAL ALTITUDE PROHIBITED ZONES                    */
+
+enum class MccAltLimitKind { MIN_ALT_LIMIT, MAX_ALT_LIMIT };
+
+template <mcc_ccte_c CCTE_T, MccAltLimitKind KIND = MccAltLimitKind::MIN_ALT_LIMIT>
+class MccAltLimitPZ : public mcc_pzone_interface_t<std::error_code>
+{
+protected:
+    double _altLimit, _cosALim, _sinAlim;
+    double _cosLat, _sinLat, _absLat;
+
+    CCTE_T* _ccteEngine;
+
+public:
+    typedef std::error_code error_t;
+
+    MccAltLimitPZ(mcc_angle_c auto const& alt_limit, mcc_angle_c auto const& latitude, CCTE_T* ccte_engine)
+        : _altLimit(alt_limit),
+          _cosALim(cos(_altLimit)),
+          _sinAlim(sin(_altLimit)),
+          _cosLat(cos(latitude)),
+          _sinLat(sin(latitude)),
+          _absLat(abs(latitude)),
+          _ccteEngine(ccte_engine)
+    {
+    }
+
+    consteval std::string_view name() const
+    {
+        return KIND == MccAltLimitKind::MIN_ALT_LIMIT   ? "MINALT-ZONE"
+               : KIND == MccAltLimitKind::MAX_ALT_LIMIT ? "MAXALT-ZONE"
+                                                        : "ALTLIMIT-UNKNOWN";
+    }
+
+
+    template <typename InputT>
+    error_t inPZone(InputT coords, bool* result)
+        requires(mcc_eqt_hrz_coord_c<InputT> || mcc_celestial_point_c<InputT>)
+    {
+        // auto ret =
+        // return ret;
+    }
+
+    template <typename InputT>
+    error_t timeToPZone(InputT coords, traits::mcc_time_duration_c auto* res_time)
+        requires(mcc_eqt_hrz_coord_c<InputT> || mcc_celestial_point_c<InputT>)
+    {
+    }
+
+    template <typename InputT>
+    error_t timeFromPZone(InputT coords, traits::mcc_time_duration_c auto* res_time)
+        requires(mcc_eqt_hrz_coord_c<InputT> || mcc_celestial_point_c<InputT>)
+    {
+    }
+
+    template <typename InputT>
+    error_t intersectPZone(InputT coords, mcc_celestial_point_c auto* point)
+        requires(mcc_eqt_hrz_coord_c<InputT> || mcc_celestial_point_c<InputT>)
+    {
+    }
+};
+
+}  // namespace mcc