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 RFCs page.

Status

RFC Template Version	(1.0)
Submission Date	October 20, 2008
Last Modified	Greg BooneTimestamp
Author	Greg Boone
RFC Status	Draft
Implementation Status	Pending
Proposed Milestone	3.4.0.0
Assigned PSC guide(s)	Greg Boone
Voting History
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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.
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.

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.
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.

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.
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.

Like the standard functions listed in RFC 8, the user can get access to the geometric function definitions via the FDO interface GetWellKnownFunctions. The new functions will be categorized as geometry functions (!FdoFunctionCategoryType_Geometry).

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.