= FDO RFC 28 -  Add Start/End Expression Functions =

This page contains a request for comments document (RFC) for the FDO Open Source project.  
More FDO RFCs can be found on the [wiki:FDORfcs RFCs] page.

== Status == 
 
||RFC Template Version||(1.0)|| 
||Submission Date||October 20, 2008||
||Last Modified||Greg Boone[[Timestamp]]||
||Author||Greg Boone||
||RFC Status||Draft||
||Implementation Status ||Pending||
||Proposed Milestone||3.4.0.0||
||Assigned PSC guide(s)||Greg Boone||
||'''Voting History'''||  ||
||+1||||
||+0||||
||-0||||
||-1||||
 
== Overview ==

This RFC follows from RFC 8 by adding geometric functions for StartX, StartY, StartZ, EndX, EndY and EndZ. 

== Signatures ==

This RFC proposes the following signatures for the new functions: 


{{{
double StartX(<geometry property>);
double StartY(<geometry property>);
double StartZ(<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: 

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 ===


{{{
FdoPtr<FdoISelect> select = (FdoISelect*)mConnection->CreateCommand (FdoCommandType_Select);
select->SetFeatureClassName (L"POLE");
FdoPtr<FdoIdentifierCollection> idColl = select->GetPropertyNames();

FdoPtr<FdoExpressionCollection> functionArgs = FdoExpressionCollection::Create();
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);
idColl->Add(computedId);

FdoPtr<FdoIFeatureReader> reader = select->Execute ();
}}}

== Affected Providers ==

This enhancement is being targeted to only affect the following providers: SDF. However, if a shared generic implementation can be designed, these functions may also be exposed through the SHP provider.

== Required FDO Enhancements ==

No FDO enhancements are required.

== Implications ==

This change will not cause any side-effects. No existing provider needs to change unless the provider wants to expose the new capability.

== Test Plan ==

Existing unit tests will be enhanced to test those changes.

== Funding/Resources ==

Autodesk to provide resource / funding to implement the feature for the affected providers.