...

cxx/mcc_mount_pec.h

@@ -28,6 +28,7 @@ class MccMountDefaultPEC final
 public:
     static constexpr MccMountType mountType = MOUNT_TYPE;
 
+    typedef std::error_code error_t;
     typedef MccAngle coord_t;
 
     struct pec_result_t {
@@ -117,11 +118,12 @@ public:
         return _pecData.type;
     }
 
-    // X and Y axis encoder coordinates
-    pec_result_t compute(const coord_t& x, const coord_t& y)
+    // The computed PEC quantities must be interpretated as:
+    //     apparent_X = encoder_X + pec_result_t.dx
+    //     apparent_Y = encoder_Y + pec_result_t.dy
+    // so, input x and y are assumed to be mount axis encoder coordinates
+    error_t compute(const coord_t& x, const coord_t& y, pec_result_t& res)
     {
-        pec_result_t res{0.0, 0.0};
-
         std::lock_guard lock(_pecDataMutex);
 
         if constexpr (mcc_is_equatorial_mount<MOUNT_TYPE>) {  // equatorial
@@ -163,7 +165,7 @@ public:
                 if (ret) {
                     res.dx = std::numeric_limits<double>::quiet_NaN();
                     res.dy = std::numeric_limits<double>::quiet_NaN();
-                    return res;
+                    return std::error_code();  // !!!!!!!!!!!!!!
                 }
 
 
@@ -173,7 +175,7 @@ public:
                 if (ret) {
                     res.dx = std::numeric_limits<double>::quiet_NaN();
                     res.dy = std::numeric_limits<double>::quiet_NaN();
-                    return res;
+                    return std::error_code();  // !!!!!!!!!!!!!!
                 }
 
 
@@ -185,9 +187,48 @@ public:
             static_assert(false, "UNSUPPORTED");
         }
 
-        return res;
+        return std::error_code();
     }
 
+    // from celestial to encoder (use of iterative scheme)
+    error_t reverseCompute(const coord_t& x, const coord_t& y, pec_result_t& res, coord_t eps, size_t max_iter = 5)
+    {
+        coord_t e2 = eps * eps;
+
+        coord_t xi = x, yi = y;
+        coord_t xp, yp;
+        size_t iter = 1;
+
+        // the first iteration
+        auto err = compute(x, y, res);
+
+        if (!err) {
+            xp = x - res.dx;
+            yp = y - res.dy;
+
+            bool ok = ((xp - x) * (xp - x) + (yp - y) * (yp - y)) <= e2;
+            if (ok) {
+                return std::error_code();
+            }
+
+            while (iter < max_iter) {
+                xi = xp;
+                yi = xp;
+                err = compute(xi, yi, res);
+                xp -= res.dx;
+                yp -= res.dy;
+
+                ok = ((xp - xi) * (xp - xi) + (yp - yi) * (yp - yi)) <= e2;
+                if (ok) {
+                    return std::error_code();
+                }
+            }
+
+            // err = "exceed max iterations";!!!
+        }
+
+        return err;
+    }
 
 
 private:
@@ -203,4 +244,7 @@ private:
 typedef MccMountDefaultPEC<MccMountType::ALTAZ_TYPE> MccMountDefaultAltAzPec;
 typedef MccMountDefaultPEC<MccMountType::FORK_TYPE> MccMountDefaultForkPec;
 
+static_assert(traits::mcc_mount_pec_c<MccMountDefaultForkPec>, "");
+
+
 }  // namespace mcc