[Shapelib] How to Extract line data with in given extents.

[Frank Warmerdam]

On Wed, 9 Feb 2005 23:38:36 +0530, Chandra Murali.S, ASDC Chennai
<chandramuralis at hcltech.com> wrote:
>  
> 
> Hi Frank, 
>         Thanks a lot for your kind reply. I've gone through this Is there
> any sample code available to accomplish this operation. 

Murali,

Do you mean the operation of comparing a SHPObject's extents
with your bounding box? 

This code from shputils.c seems to compare SHPObject psCShape to 
a bounding box defined by cxmin,cymin,cxmax,cymax. 

       /*** FIRST check the boundary of the feature ***/
       if ( ( (psCShape->dfXMin < cxmin) && (psCShape->dfXMax < cxmin) ) ||
            ( (psCShape->dfYMin < cymin) && (psCShape->dfYMax < cymin) ) ||
            ( (psCShape->dfXMin > cxmax) && (psCShape->dfXMax > cxmax) ) ||
            ( (psCShape->dfYMin > cymax) && (psCShape->dfYMax > cymax) ) )
            {   /** Feature is totally outside clip area **/
            	if (ierase) return(1); /** WRITE RECORD **/
            	     else   return(0); /** SKIP  RECORD **/
            }

There is actually a bunch more "clipping to rectangle" code in the same function
(clip_boundary() in shputils.c) that might be of interest. 

Best regards,
-- 
---------------------------------------+--------------------------------------
I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush    | Geospatial Programmer for Rent