[Mapserver-users] Shapelib, GPC, PHP, and polygon clipping

[Carl Anderson]

On 04/30/2004 08:38:04 PM, "Ryan, Adam" wrote:
> 
> Steve, Frank, etc...
> 
> A while back Steve Lime wrote in response to a request for polygon
> clipping
> code.
> 
> http://mapserver.gis.umn.edu/data2/wilma/mapserver-users/0201/msg00094.html
> 
> He suggested using the GPC library.  I checked this out and was able
> to get
> it to work.
> 
> Is it worth trying to use GPC with either PHP mapscript or shapelib
> directly
> and  write a little routine to grab the shapes in question, convert
> them to
> gpc ascii format, run the clip operation, and convert back to a
> shapefile
> result?  In PHP I could build the ASCII files, then call a gpc
> executable,
> and then translate the ASCII result back into a new shapefile.
>


I did that I while back and found that about 0.5% of  clipped polygons
were collected wrong from the base shapes.  Not a big number but  
overtime it builds up....

either JTS (JAVA,  http://www.vividsolutions.com/jts/) or GEOS
(C++, http://geos.refractions.net) are a better starting point

C.