Index: trunk/archive/pslib/include/psPosition.h
===================================================================
--- trunk/archive/pslib/include/psPosition.h	(revision 251)
+++ trunk/archive/pslib/include/psPosition.h	(revision 253)
@@ -7,33 +7,40 @@
  */
 
-/*************************************************/
+/** A point in 2-D space, with errors.
+ */
 typedef struct {
     union {
 	double x;				//!< x position
 	double r;				//!< x position
-    }
+    } x;
     union {
 	double xErr;				//!< Error in x position
 	double rErr;				//!< Error in x position
-    }
+    } dx;
     union {
 	double y;				//!< y position
 	double d;				//!< y position
-    }
+    } y;
     union {
 	double yErr;				//!< Error in y position
 	double dErr;				//!< Error in y position
-    }
+    } dy;
 } psCoord;
 
+/** A polynomial transformation between coordinate frames.  This may be a linear relationship, or may
+ * represent a higher-order transformation.
+ */
+typedef struct {
+    psDPolynomial2D *x;
+    psDPolynomial2D *y;
+} psCoordXform;
+
+/** The optical distortion terms.  The lowest two terms are the x and y axis of the target system.  The higher
+ * two terms represent magnitude and color terms.
+ */
 typedef struct {
     psDPolynomial4D *x;
     psDPolynomial4D *y;
 } psDistortion;
-
-typedef struct {
-    psDPolynomial2D *x;
-    psDPolynomial2D *y;
-} psCoordXform;
 
 psCoord *psCoordXformApply (psCoordXform *frame, psCoord *coords);
@@ -46,14 +53,14 @@
 
 /** Get offset (RA,Dec) on the sky between two positions position1 and position2 may not be identical */
-psCoords *
-psGetOffset(const psCoords *restrict position1, //!< Position 1
-	    const psCoords *restrict position2, //!< Position 2
+psCoord *
+psGetOffset(const psCoord *restrict position1, //!< Position 1
+	    const psCoord *restrict position2, //!< Position 2
 	    char *system
 	    );
 
 /** Apply an offset to a position */
-psCoords *
-psApplyOffset(const psCoords *restrict position, //!< Position
-	      const psCoords *restrict offset, //!< Offset
+psCoord *
+psApplyOffset(const psCoord *restrict position, //!< Position
+	      const psCoord *restrict offset, //!< Offset
 	      char *system
     );
@@ -64,10 +71,10 @@
 
 /** Get Sun Position */
-psCoords *
+psCoord *
 psGetSunPos(float mjd			//!< MJD to get position for
 	    );
 
 /** Get Moon position */
-psCoords *
+psCoord *
 psGetMoonPos(float mjd,			//!< MJD to get position for
 	     double latitude,		//!< Latitude for apparent position
@@ -81,5 +88,5 @@
 
 /** Get Planet positions */
-psCoords *
+psCoord *
 psGetSolarSystemPos(char *solarSystemObject, //!< Named S.S. object
 		    float mjd		//!< MJD to get position for