[geos-devel] Re: GEOS / SRID / WKB

[strk at refractions.net]

On Thu, Feb 02, 2006 at 01:26:33AM -0700, Charlie Savage wrote:
> Hi Strk,
> 
> Yes, that sounds like a good way of doing it.  Is this planned for the 
> near future, or should I  put something together if I need it?

No plans for near future.
I think that should also include support for M, and
GEOS is not ready for that yet.

> What do you think of saving the SRID on input (i.e., accepting 
> extensions)?  That's the part that I need at the moment.

The Geometry class provides a setUserData/getUserData mechanism
for extended informations to be added to a Geometry. 
Maybe that's a better way to handle this, as the setSRID/getSRID
methods have been marked as deprecated.

--strk;


> 
> Thanks,
> 
> Charlie
> 
> strk at refractions.net wrote:
> >Charlie, we're playing dirty here, even for Z values.
> >One thing is accepting "extensions", another thing is spitting them out.
> >Z,M and SRID flags are postgis-specific.
> >The next update on OGC dox will define a different way to express
> >Z and M for example, and won't say anything about SRID.
> >
> >The most correct way to support multiple different specs
> >would be to provide a method to specify which one to use.
> >
> >For example:
> >
> >	WKBWriter writer;
> >	writer.setFormat(DIALECT);
> >	writer.write(geom);
> >
> >Same would apply to WKBReader and to WKT reader/writer.
> >
> >--strk;
> >
> >On Wed, Feb 01, 2006 at 06:50:07PM -0700, Charlie Savage wrote:
> >  
> >>I'd like to be able to read/write SRID information from GEOS using the 
> >>WKB Reader/Writer.  Currently the WKBReader reads the SRID value in an 
> >>extended WKB format, but then tosses it away.  Attached is a patch that 
> >>saves the SRID value by calling setSRID on the newly created geometry. 
> >>
> >>It would also be nice if WKBWriter could output SRID values.  Looking 
> >>through the code, it would be easy enough to write this information 
> >>out.  However, if a geometry has an SRID, the output WKB value would be 
> >>one byte longer plus have an SRID flag in the geomtype byte.  So this 
> >>would break existing code that reads wkb values if a geometry has an 
> >>SRID.  I'm not sure if this is an issue or not, since I see the SRID 
> >>field on a geometry is not documented.  Is this a frequently used 
> >>feature?  An alternative of course would be having a separate method, 
> >>maybe called writeExtended or some such thing.  
> >>
> >>Thanks,
> >>
> >>Charlie
> >>    
> >
> >  
> >>Index: source/io/WKBReader.cpp
> >>===================================================================
> >>RCS file: /home/cvs/postgis/geos/source/io/WKBReader.cpp,v
> >>retrieving revision 1.15
> >>diff -u -r1.15 WKBReader.cpp
> >>--- source/io/WKBReader.cpp	20 Jan 2006 00:59:55 -0000	1.15
> >>+++ source/io/WKBReader.cpp	2 Feb 2006 01:44:16 -0000
> >>@@ -230,31 +230,43 @@
> >> 	cout<<"WKB hasSRID: "<<hasZ<<endl;
> >> #endif
> >> 
> >>-	if (hasSRID) dis.readInt(); // skip SRID
> >>-
> >>+	int srid = -1;
> >>+	if (hasSRID) srid = dis.readInt(); // read SRID
> >> 
> >> 	// allocate space for ordValues 
> >> 	if ( ordValues.size() < inputDimension )
> >> 		ordValues.resize(inputDimension);
> >> 
> >>+	Geometry * result;
> >> 
> >> 	switch (geometryType) {
> >> 		case WKBConstants::wkbPoint :
> >>-			return readPoint();
> >>+			result = readPoint();
> >>+			break;
> >> 		case WKBConstants::wkbLineString :
> >>-			return readLineString();
> >>+			result = readLineString();
> >>+			break;
> >> 		case WKBConstants::wkbPolygon :
> >>-			return readPolygon();
> >>+			result = readPolygon();
> >>+			break;
> >> 		case WKBConstants::wkbMultiPoint :
> >>-			return readMultiPoint();
> >>+			result = readMultiPoint();
> >>+			break;
> >> 		case WKBConstants::wkbMultiLineString :
> >>-			return readMultiLineString();
> >>+			result = readMultiLineString();
> >>+			break;
> >> 		case WKBConstants::wkbMultiPolygon :
> >>-			return readMultiPolygon();
> >>+			result = readMultiPolygon();
> >>+			break;
> >> 		case WKBConstants::wkbGeometryCollection :
> >>-			return readGeometryCollection();
> >>+			result = readGeometryCollection();
> >>+			break;
> >>+		default:
> >>+			throw new ParseException("Unknown WKB type " + 
> >>geometryType);
> >> 	}
> >>-	throw new ParseException("Unknown WKB type " + geometryType);
> >>+
> >>+	result->setSRID(srid);
> >>+	return result;
> >> }
> >> 
> >> Point *
> >>
> >>    
> >
> >
> >
> >
> >  



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