C: Added Astronomy_VectorFromEquator and Astronomy_EquatorFromVector.

These helper routines in the JavaScript code make sense for C also.

generate/ctest.c

@@ -2167,8 +2167,7 @@ static int Test_EQJ_EQD(astro_body_t body)
 {
     astro_time_t time;
     astro_observer_t observer;
-    astro_equatorial_t eq2000, eqdate;
-    astro_spherical_t sphere;
+    astro_equatorial_t eq2000, eqdate, eqcheck;
     astro_vector_t v2000, vdate, t2000;
     astro_rotation_t r;
     double ra_diff, dec_diff, dist_diff, diff;
@@ -2184,12 +2183,8 @@ static int Test_EQJ_EQD(astro_body_t body)
     eqdate = Astronomy_Equator(body, &time, observer, EQUATOR_OF_DATE, ABERRATION);
     CHECK_STATUS(eqdate);
 
-    /* Convert EQJ spherical coordinates to vector. */
-    sphere.status = ASTRO_SUCCESS;
-    sphere.lat = eq2000.dec;
-    sphere.lon = 15.0 * eq2000.ra;
-    sphere.dist = eq2000.dist;
-    v2000 = Astronomy_VectorFromSphere(sphere, time);
+    /* Convert EQJ angular coordinates to vector. */
+    v2000 = Astronomy_VectorFromEquator(eq2000, time);
     CHECK_STATUS(v2000);
 
     /* Find rotation matrix. */
@@ -2200,14 +2195,14 @@ static int Test_EQJ_EQD(astro_body_t body)
     vdate = Astronomy_RotateVector(r, v2000);
     CHECK_STATUS(vdate);
 
-    /* Convert vector back to spherical coordinates. */
-    sphere = Astronomy_SphereFromVector(vdate);
-    CHECK_STATUS(sphere);
+    /* Convert vector back to angular coordinates. */
+    eqcheck = Astronomy_EquatorFromVector(vdate);
+    CHECK_STATUS(eqcheck);
 
     /* Compare the result with the eqdate. */
-    ra_diff = fabs((sphere.lon / 15.0) - eqdate.ra);
-    dec_diff = fabs(sphere.lat - eqdate.dec);
-    dist_diff = fabs(sphere.dist - eqdate.dist);
+    ra_diff = fabs(eqcheck.ra - eqdate.ra);
+    dec_diff = fabs(eqcheck.dec - eqdate.dec);
+    dist_diff = fabs(eqcheck.dist - eqdate.dist);
     printf("Test_EQJ_EQD: %s ra=%0.3lf, dec=%0.3lf, dist=%0.3lf, ra_diff=%lg, dec_diff=%lg, dist_diff=%lg\n", Astronomy_BodyName(body), eqdate.ra, eqdate.dec, eqdate.dist, ra_diff, dec_diff, dist_diff);
     if (ra_diff > 1.0e-14 || dec_diff > 1.0e-14 || dist_diff > 4.0e-15)
     {
@@ -2240,8 +2235,8 @@ static int Test_EQD_HOR(astro_body_t body)
     astro_equatorial_t eqd, eqj;
     astro_horizon_t hor;
     astro_rotation_t rot;
-    astro_vector_t vec_eqd, vec_eqj, vec_hor, check_eqd, check_eqj, check_hor;
     astro_spherical_t sphere;
+    astro_vector_t vec_eqd, vec_eqj, vec_hor, check_eqd, check_eqj, check_hor;
     double diff_az, diff_alt, diff;
     int error;
 
@@ -2253,11 +2248,7 @@ static int Test_EQD_HOR(astro_body_t body)
     hor = Astronomy_Horizon(&time, observer, eqd.ra, eqd.dec, REFRACTION_NORMAL);
 
     /* Calculate the position of the body as an equatorial vector of date. */
-    sphere.status = ASTRO_SUCCESS;
-    sphere.dist = eqd.dist;
-    sphere.lat = eqd.dec;
-    sphere.lon = 15.0 * eqd.ra;
-    CHECK_VECTOR(vec_eqd, Astronomy_VectorFromSphere(sphere, time));
+    CHECK_VECTOR(vec_eqd, Astronomy_VectorFromEquator(eqd, time));
 
     /* Calculate rotation matrix to convert equatorial J2000 vector to horizontal vector. */
     rot = Astronomy_Rotation_EQD_HOR(time, observer);
@@ -2306,11 +2297,7 @@ static int Test_EQD_HOR(astro_body_t body)
 
     /* Exercise HOR to EQJ translation. */
     CHECK_EQU(eqj, Astronomy_Equator(body, &time, observer, EQUATOR_J2000, ABERRATION));
-    sphere.status = ASTRO_SUCCESS;
-    sphere.dist = eqj.dist;
-    sphere.lat = eqj.dec;
-    sphere.lon = 15.0 * eqj.ra;
-    CHECK_VECTOR(vec_eqj, Astronomy_VectorFromSphere(sphere, time));
+    CHECK_VECTOR(vec_eqj, Astronomy_VectorFromEquator(eqj, time));
 
     rot = Astronomy_Rotation_HOR_EQJ(time, observer);
     CHECK_ROTMAT(rot);

generate/template/astronomy.c

@@ -4210,6 +4210,64 @@ astro_spherical_t Astronomy_SphereFromVector(astro_vector_t vector)
     return sphere;
 }
 
+
+/**
+ * @brief
+ *  Given angular equatorial coordinates in `equ`, calculates equatorial vector.
+ *
+ * @param equ
+ *      An object that contains angular equatorial coordinates to be converted to a vector.
+ *
+ * @param time
+ *      The date and time of the observation. This is needed because the returned
+ *      vector object requires a valid time value when passed to certain other functions.
+ *
+ * @return
+ *      A vector in the equatorial system.
+ */
+astro_vector_t Astronomy_VectorFromEquator(astro_equatorial_t equ, astro_time_t time)
+{
+    astro_spherical_t sphere;
+
+    if (equ.status != ASTRO_SUCCESS)
+        return VecError(ASTRO_INVALID_PARAMETER, time);
+
+    sphere.status = ASTRO_SUCCESS;
+    sphere.lat = equ.dec;
+    sphere.lon = 15.0 * equ.ra;     /* convert sidereal hours to degrees */
+    sphere.dist = equ.dist;
+
+    return Astronomy_VectorFromSphere(sphere, time);
+}
+
+
+/**
+ * Given an equatorial vector, calculates equatorial angular coordinates.
+ *
+ * @param vector
+ *      A vector in an equatorial coordinate system.
+ *
+ * @return
+ *      Angular coordinates expressed in the same equatorial system as `vec`.
+ */
+astro_equatorial_t Astronomy_EquatorFromVector(astro_vector_t vector)
+{
+    astro_equatorial_t equ;
+    astro_spherical_t sphere;
+
+    sphere = Astronomy_SphereFromVector(vector);
+    if (sphere.status != ASTRO_SUCCESS)
+        return EquError(sphere.status);
+
+    equ.status = ASTRO_SUCCESS;
+    equ.dec = sphere.lat;
+    equ.ra = sphere.lon / 15.0;     /* convert degrees to sidereal hours */
+    equ.dist = sphere.dist;
+
+    return equ;
+}
+
+
 static double ToggleAzimuthDirection(double az)
 {
     az = 360.0 - az;

generate/template/astronomy.js

@@ -3354,7 +3354,7 @@ Astronomy.VectorFromSphere = function(sphere, time) {
 }
 
 /**
- * Given angular equatorial coordinates in `sphere`, calculates equatorial vector.
+ * Given angular equatorial coordinates in `equ`, calculates equatorial vector.
  *
  * @param {Astronomy.EquatorialCoordinates} equ
  *      An object that contains angular equatorial coordinates to be converted to a vector.

source/c/README.md

@@ -354,6 +354,28 @@ Correction for aberration is optional, using the `aberration` parameter.
 
 
 
+---
+
+<a name="Astronomy_EquatorFromVector"></a>
+### Astronomy_EquatorFromVector(vector) &#8658; [`astro_equatorial_t`](#astro_equatorial_t)
+
+
+
+Given an equatorial vector, calculates equatorial angular coordinates.
+
+
+
+**Returns:**  Angular coordinates expressed in the same equatorial system as `vec`. 
+
+
+
+| Type | Parameter | Description |
+| --- | --- | --- |
+| [`astro_vector_t`](#astro_vector_t) | `vector` |  A vector in an equatorial coordinate system. | 
+
+
+
+
 ---
 
 <a name="Astronomy_GeoMoon"></a>
@@ -1558,6 +1580,29 @@ After calculating the date and time of an astronomical event in the form of an [
 
 
 
+---
+
+<a name="Astronomy_VectorFromEquator"></a>
+### Astronomy_VectorFromEquator(equ, time) &#8658; [`astro_vector_t`](#astro_vector_t)
+
+**Given angular equatorial coordinates in `equ`, calculates equatorial vector.** 
+
+
+
+
+
+**Returns:**  A vector in the equatorial system. 
+
+
+
+| Type | Parameter | Description |
+| --- | --- | --- |
+| [`astro_equatorial_t`](#astro_equatorial_t) | `equ` |  An object that contains angular equatorial coordinates to be converted to a vector. | 
+| [`astro_time_t`](#astro_time_t) | `time` |  The date and time of the observation. This is needed because the returned vector object requires a valid time value when passed to certain other functions. | 
+
+
+
+
 ---
 
 <a name="Astronomy_VectorFromHorizon"></a>

source/c/astronomy.c

@@ -5449,6 +5449,64 @@ astro_spherical_t Astronomy_SphereFromVector(astro_vector_t vector)
     return sphere;
 }
 
+
+/**
+ * @brief
+ *  Given angular equatorial coordinates in `equ`, calculates equatorial vector.
+ *
+ * @param equ
+ *      An object that contains angular equatorial coordinates to be converted to a vector.
+ *
+ * @param time
+ *      The date and time of the observation. This is needed because the returned
+ *      vector object requires a valid time value when passed to certain other functions.
+ *
+ * @return
+ *      A vector in the equatorial system.
+ */
+astro_vector_t Astronomy_VectorFromEquator(astro_equatorial_t equ, astro_time_t time)
+{
+    astro_spherical_t sphere;
+
+    if (equ.status != ASTRO_SUCCESS)
+        return VecError(ASTRO_INVALID_PARAMETER, time);
+
+    sphere.status = ASTRO_SUCCESS;
+    sphere.lat = equ.dec;
+    sphere.lon = 15.0 * equ.ra;     /* convert sidereal hours to degrees */
+    sphere.dist = equ.dist;
+
+    return Astronomy_VectorFromSphere(sphere, time);
+}
+
+
+/**
+ * Given an equatorial vector, calculates equatorial angular coordinates.
+ *
+ * @param vector
+ *      A vector in an equatorial coordinate system.
+ *
+ * @return
+ *      Angular coordinates expressed in the same equatorial system as `vec`.
+ */
+astro_equatorial_t Astronomy_EquatorFromVector(astro_vector_t vector)
+{
+    astro_equatorial_t equ;
+    astro_spherical_t sphere;
+
+    sphere = Astronomy_SphereFromVector(vector);
+    if (sphere.status != ASTRO_SUCCESS)
+        return EquError(sphere.status);
+
+    equ.status = ASTRO_SUCCESS;
+    equ.dec = sphere.lat;
+    equ.ra = sphere.lon / 15.0;     /* convert degrees to sidereal hours */
+    equ.dist = sphere.dist;
+
+    return equ;
+}
+
+
 static double ToggleAzimuthDirection(double az)
 {
     az = 360.0 - az;

source/c/astronomy.h

@@ -616,8 +616,10 @@ astro_rotation_t Astronomy_InverseRotation(astro_rotation_t rotation);
 astro_rotation_t Astronomy_CombineRotation(astro_rotation_t a, astro_rotation_t b);
 astro_vector_t Astronomy_VectorFromSphere(astro_spherical_t sphere, astro_time_t time);
 astro_spherical_t Astronomy_SphereFromVector(astro_vector_t vector);
-astro_spherical_t Astronomy_HorizonFromVector(astro_vector_t vector, astro_refraction_t refraction);
+astro_vector_t Astronomy_VectorFromEquator(astro_equatorial_t equ, astro_time_t time);
+astro_equatorial_t Astronomy_EquatorFromVector(astro_vector_t vector);
 astro_vector_t Astronomy_VectorFromHorizon(astro_spherical_t sphere, astro_time_t time, astro_refraction_t refraction);
+astro_spherical_t Astronomy_HorizonFromVector(astro_vector_t vector, astro_refraction_t refraction);
 astro_vector_t Astronomy_RotateVector(astro_rotation_t rotation, astro_vector_t vector);
 
 astro_rotation_t Astronomy_Rotation_EQD_EQJ(astro_time_t time);

source/js/README.md

@@ -1149,7 +1149,7 @@ includes the time, as required by <code>AstroTime</code>.
 <a name="Astronomy.VectorFromEquator"></a>
 
 ### Astronomy.VectorFromEquator(equ, time) ⇒ [<code>Vector</code>](#Astronomy.Vector)
-Given angular equatorial coordinates in `sphere`, calculates equatorial vector.
+Given angular equatorial coordinates in `equ`, calculates equatorial vector.
 
 **Kind**: static method of [<code>Astronomy</code>](#Astronomy)  
 **Returns**: [<code>Vector</code>](#Astronomy.Vector) - A vector in the equatorial system.  

source/js/astronomy.js

@@ -4375,7 +4375,7 @@ Astronomy.VectorFromSphere = function(sphere, time) {
 }
 
 /**
- * Given angular equatorial coordinates in `sphere`, calculates equatorial vector.
+ * Given angular equatorial coordinates in `equ`, calculates equatorial vector.
  *
  * @param {Astronomy.EquatorialCoordinates} equ
  *      An object that contains angular equatorial coordinates to be converted to a vector.