Changes between Version 16 and Version 17 of FDORfc28

Timestamp:

11/05/08 12:11:19 (16 years ago)

Author:

robertfortin

Comment:

--

FDORfc28

@@ -8 +8 @@
 ||RFC Template Version||(1.0)|| 
 ||Submission Date||October 20, 2008||
-||Last Modified||Greg Boone[[Timestamp]]||
+||Last Modified||Robert Fortin[[Timestamp]]||
 ||Author||Greg Boone||
 ||RFC Status||Draft||
@@ -22 +22 @@
 == Overview ==
 
-This RFC follows from RFC 8 by adding geometric functions for StartX, StartY, StartZ, EndX, EndY and EndZ. 
+This RFC follows from RFC 8 by adding geometric functions to retrieve the X, Y, Z and M value of a point.
 
 == Signatures ==
@@ -30 +30 @@
 
 {{{
-double StartX(<geometry property>);
-double StartY(<geometry property>);
-double StartZ(<geometry property>);
+double X(<geometry property>);
+double Y(<geometry property>);
+double Z(<geometry property>);
+double M(<geometry property>);
 
-double EndX(<geometry property>);
-double EndY(<geometry property>);
-double EndZ(<geometry property>);
 }}}
 
-All of the above functions accept a geometry property only. The result of the functions depend on the provided geometry: 
+All of the above functions accept a geometry property of type point only. if the geometry is not a point or if the dimension of the geometry prevent from returning a proper value (e.g. Z() function on a 2D geometry), a null value is returned. 
 
-If the provided geometry is a point geometry, the result of the Start/End functions is the x, y, z values of the point.[[BR]]
-If the provided geometry is a multi-point geometry, the result of the Start/End functions is the x, y, z values of the first point.[[BR]]
-
-If the provided geometry is a line geometry, the result of the Start/End functions is the x, y, z values of the start and end points of the first line.[[BR]]
-If the provided geometry is a multi-line geometry, the result of the Start/End functions is the x, y, z values of the start and end points of the first line.[[BR]]
-
-If the provided geometry is a polygon geometry, the result of the Start/End functions is the x, y, z values of the start and end points of the exterior ring of the polygon.[[BR]]
-If the provided geometry is a multi-polygon geometry, the result of the Start/End functions is the x, y, z values of the start and end points of the exterior ring of the first polygon.[[BR]]
 
 === Example ===
@@ -61 +51 @@
 FdoPtr<FdoIdentifier> arg1 = FdoIdentifier::Create(L"GEOMETRY");
 functionArgs->Add(arg1);
-FdoPtr<FdoFunction> expr = FdoFunction::Create(L"STARTX", functionArgs);
-FdoPtr<FdoComputedIdentifier> computedId = FdoComputedIdentifier::Create(L"POLE_STARTX", expr);
+FdoPtr<FdoFunction> expr = FdoFunction::Create(L"X", functionArgs);
+FdoPtr<FdoComputedIdentifier> computedId = FdoComputedIdentifier::Create(L"POLE_X", expr);
 idColl->Add(computedId);
 
 FdoPtr<FdoIFeatureReader> reader = select->Execute ();
 }}}
+
+== Standard Considerations ==
+
+During the initial proposal of this RFC (which was focusing on returning the StartX/Y/Z and EndX/Y/Z of any geometry),  many altertives were considered.  The concensus was that fdo should try to use an existing standard.  The function signature adopted here are based on the OGC [http://www.opengeospatial.org/standards/sfa Simple Feature Access] standard.
+
+Other functions were considered for the initial RFC proposal but are __outside the scope__ of this RFC:
+
+   !StartPoint(): Point[[BR]]
+   !EndPoint(): Point[[BR]]
+   !NumPoints(): Int[[BR]]
+   PointN(N): Point[[BR]]
+
+
+Using these additional functions in combination with the X,Y,Z and M functions, it would have been possible to return the start and end coordinate for other type of geometry.
+
+Example:
+   To retrieve the X value for the first point of a line -->  X(!StartPoint(<geometry>) or X(PointN(1, <geometry>)[[BR]]
+   To retrieve the Y value for the last point of a line -->  Y(!EndPoint(<geometry>) or X(PointN(!NumPoints(<geometry>, <geometry>)[[BR]]
+
+
 
 == Affected Providers ==