[fdo-internals] Request review of RFC 28 - AddStart/EndExpressionFunctions

[Maksim Sestic]

Why don't you introduce optional parameter for vertice index being
inspected, i.e. PointX(n) - if there's no parameter then value of 0 is
assumed (used with Point geometries). In that way one can evaluate
linestring and polygon single vertice coordinate.
 
I think there's something else missing - I'm trying to draw directions for
one-way roads, as in Google Earth/Map. Although each road network's
linestring is directed (as in directed graph) and has direction flag
attached (uni/bi-directional), I still don't have enough data to actually
rotate an arrow - depicting road direction. How about introducing AngleXY()
and AngleXY(n) functions returning line segment angle in plane? Is there any
other solution to this, except for storing pre-calculated vectors? Maybe
adding some additional stylization rule for this?
 
Regards,
Maksim Sestic

  _____  

From: fdo-internals-bounces at lists.osgeo.org
[mailto:fdo-internals-bounces at lists.osgeo.org] On Behalf Of Traian Stanev
Sent: Monday, November 03, 2008 23:40
To: FDO Internals Mail List
Subject: RE: [fdo-internals] Request review of RFC 28 -
AddStart/EndExpressionFunctions



Yeah, may be just provide PointX()/PointY()/PointZ() functions which take a
geometry as argument and throw an error for anything but points?

 

Traian

 

From: fdo-internals-bounces at lists.osgeo.org
[mailto:fdo-internals-bounces at lists.osgeo.org] On Behalf Of Dan Stoica
Sent: Monday, November 03, 2008 5:24 PM
To: FDO Internals Mail List
Subject: RE: [fdo-internals] Request review of RFC 28 - Add
Start/EndExpressionFunctions

 

What has the Start point so special except for the point features? For
example, the START=END for simple polygons. 

Maybe this ECO should address only points? 

 

Dan.

 

From: fdo-internals-bounces at lists.osgeo.org
[mailto:fdo-internals-bounces at lists.osgeo.org] On Behalf Of Greg Boone
Sent: Monday, November 03, 2008 2:53 PM
To: FDO Internals Mail List
Subject: RE: [fdo-internals] Request review of RFC 28 - Add
Start/EndExpressionFunctions

 

Yes, Lines and Polygons do offer some difficulties. Also, the multi-geometry
objects are also a little weird. I am open to suggestions on how to handle
these types.

 

Greg

 

From: fdo-internals-bounces at lists.osgeo.org
[mailto:fdo-internals-bounces at lists.osgeo.org] On Behalf Of Jason Birch
Sent: Thursday, October 23, 2008 12:34 PM
To: FDO Internals Mail List
Subject: RE: [fdo-internals] Request review of RFC 28 - Add
Start/EndExpressionFunctions

 

That makes sense to me; I just wasn't sure what you would use the equivalent
function for lines/polygons for.

 

Jason 

 

From: Robert Fortin
Subject: RE: [fdo-internals] Request review of RFC 28 - Add
Start/EndExpressionFunctions

 

The use case: presents the ordinates of a point geometry as attribute in a
data table.  This feature will help us achieve that.

You could also think it can be used to display the coordinate as labels as
part of the symbology of a feature.  

Or you could use the StartZ to show the elevation of a point or apply a
theme on it.

All these can't be done easily directly using the geometry attribute.

 



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