[geos-devel] GEOS SRID Patch

Howard Butler hobu.inc at gmail.com
Wed Sep 19 00:05:34 EDT 2007

Do we need to increment the API with these additions?  What policy  
did Sandro have going?


On Sep 18, 2007, at 10:51 PM, Charlie Savage wrote:

> So - any comments on this.  Will people get upset if I commit it  
> (which I would like to do)?
> Charlie
> Charlie Savage wrote:
>> I've attached a patch that implements what we discussed yesterday.
>> More specifically:
>> * It updates WkbWriter to support outputting SRID values in EWKB/ 
>> HEX format.  This is off by default so is backwards compatible.
>> * Adds getter/setter methods for byte order, dimensions and  
>> include SRID to WkbWriter - these are needed for the C API changes  
>> below.
>> * Adds new C API interfaces for WktReader, WktWriter, WkbReader,  
>> WkbWriter.  These were added to the end of the *.h file and I did  
>> not change any existing C apis - so this should be backwards  
>> compatible.
>> Here is what the new WkbWriter interface, which is the most  
>> complicated one, looks like:
>> extern GEOSWKBWriter GEOS_DLL *GEOSWKBWriter_create();
>> extern void GEOS_DLL GEOSWKBWriter_destroy(GEOSWKBWriter* writer);
>> extern unsigned char GEOS_DLL *GEOSWKBWriter_write(GEOSWKBWriter*  
>> writer, const GEOSGeometry* g, size_t *size);
>> extern unsigned char GEOS_DLL *GEOSWKBWriter_writeHEX 
>> (GEOSWKBWriter* writer, const GEOSGeometry* g, size_t *size);
>> extern int GEOS_DLL GEOSWKBWriter_getOutputDimension(const  
>> GEOSWKBWriter* writer);
>> extern void GEOS_DLL GEOSWKBWriter_setOutputDimension 
>> (GEOSWKBWriter* writer, int newDimension);
>> extern int GEOS_DLL GEOSWKBWriter_getByteOrder(const  
>> GEOSWKBWriter* writer);
>> extern void GEOS_DLL GEOSWKBWriter_setByteOrder(GEOSWKBWriter*  
>> writer, int byteOrder);
>> extern char GEOS_DLL GEOSWKBWriter_getIncludeSRID(const  
>> GEOSWKBWriter* writer);
>> extern void GEOS_DLL GEOSWKBWriter_setIncludeSRID(GEOSWKBWriter*  
>> writer, const char writeSRID);
>> Here is some example ruby code that uses the new api via SWIG:
>> writer = Geos::WktWriter.new
>> writer.includes_srid = true
>> writer.output_dimension = 3
>> wkb = writer.write(geom)
>> hex = writer.write_hex(geom)
>> The other readers/writers work similarly.
>> I think this is a better approach then the current API because:
>> 1.  It eliminates the need for the hacky static variables for byte  
>> order and output dimensions
>> 2.  It gives the client more control - you can create a reader/ 
>> writer and reuse it instead of having a new one created every time  
>> you read/write a geometry
>> 3.  Its more extensible.  For example, at some point we may wish  
>> that the WktReader supports the EWKT format.  That would require  
>> doing this:
>> extern char GEOS_DLL GEOSWKTWriter_getIncludeSRID(const  
>> GEOSWKTWriter* writer);
>> extern void GEOS_DLL GEOSWKTWriter_setIncludeSRID(GEOSWKTWriter*  
>> writer, const char writeSRID);
>> So I think this patch meets my objectives (more client control,  
>> supports outputting SRID values), Frank's objectives (get rid of  
>> static fields) and Paul's (backwards compatible).
>> I also tested it by exposing the new API via SWIG and updating the  
>> various Ruby tests I have.  So at least every new method has been  
>> called/verified via a simple set of tests.
>> Comments?  If this looks ok, can I apply it?
>> Charlie
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