Merge pull request #32 from pdowler/master

coordinate limits more flexible to allow for other coordinate systems

DALI.tex

@@ -747,26 +747,28 @@ \subsection{Point}
 12.3 45.6
 \end{verbatim}
 
-In spherical coordinates, all longitude values must fall within [0,360] and all
-latitude values within [-90,90].
+Coordinate values are not limited to fall within a defined valid range; this is a change from
+DALI 1.1 where equatorial coordinates were explicitly limited. Software may have
+to perform range reduction in some coordinate systems (for example, spherical coordinates) in 
+order to correctly interpret or use the coordinate values. Coordinate values are more likely to
+work as expected if they are expressed in the simplest form and do not require range reduction.
+For example, in spherical coordinates, \verb|362.0 2.0| is equivalent to \verb|2.0 2.0|, but the
+latter form is more likely to work as intended in all cases.
 
 There is no general purpose definition of minimum and/or maximum point values, but
 specific services may define something that is applicable in a more limited context.
 
 \subsection{Circle}
 Circle values serialised in VOTable or service parameters must have the following metadata in the
 \xmlel{FIELD} element: \verb|datatype="double"| or \verb|datatype="float"|, \verb|arraysize="3"|,
-\verb|xtype="circle"|. For circles
-in a spherical coordinate system, the values are ordered as: longitude latitude
-radius; longitude values must fall within [0,360], latitude values
-within [-90,90], and radius values in (0,180]. For example:
+\verb|xtype="circle"|. 
+The values are ordered as a point followed by a radius. For example:
 
 \begin{verbatim}
 12.3 45.6 0.5
 \end{verbatim}
 
-In spherical coordinates, all longitude values must fall within [0,360] and all
-latitude values within [-90,90].
+Valid coordinate value limits are specified by \verb|xtype="point"| above.
 
 Circle-valued service parameters may include additional metadata like minimum and
 or maximum value. These are specified using a custom interpretation of the
@@ -795,11 +797,12 @@ \subsection{Range}
 
 includes values from 10 to 11 (coordinate1) and from 20 to 21 (coordinate2).
 
-In spherical coordinates, coordinates are longitude followed by latitude; longitude values must
-fall within [0,360] and all latitude values within [-90,90]. This range form is used as part of
-the value of the POS parameter in \citep{2015ivoa.spec.1223D} and \citep{2017ivoa.spec.0517B}
-(see also "shape" below). A range can span the meridian (longitude 0): 359 1 -1 1 is interpreted
-as the small (2x2 degree) coordinate range from 359 across the meridian to 1 degree longitude.
+Valid coordinate value limits are specified by \verb|xtype="point"| above. 
+This range form is used as part of the value of the POS parameter in 
+\citep{2015ivoa.spec.1223D} and \citep{2017ivoa.spec.0517B} (see also "shape" below). 
+For example, a range can span the meridian (longitude 0): 359 1 -1 1 is interpreted
+as the small (2x2 degree) coordinate range from 359 across the meridian to 1 degree 
+longitude.
 
 Range-valued service parameters may include additional metadata like minimum and
 or maximum value. These are specified using a custom interpretation of the
@@ -828,8 +831,8 @@ \subsection{Polygon}
 10.0 10.0 10.2 10.0 10.2 10.2 10.0 10.2
 \end{verbatim}
 
-In spherical coordinates, all longitude values must fall within [0,360] and all
-latitude values within [-90,90]. Vertices must be ordered such that the polygon
+Valid coordinate value limits are specified by \verb|xtype="point"| above. 
+Vertices must be ordered such that the polygon
 winding direction is counter-clockwise (when viewed from the origin toward the
 sky) as described in \citep{2007ivoa.spec.1030R}.