[Ottawa_users] Clipping shapefiles with ogr2ogr

[Paul Spencer]

My first guess is that ogr2ogr doesn't clip, it uses the bbox as a  
spatial selection and keeps anything that intersects with the bbox.   
Would this account for your results?

Paul

On 17-Feb-08, at 9:25 PM, Alyre Chiasson wrote:

> Hello,
>
> I have two shape files with the following identical prj :
>
> GEOGCS 
> ["GCS_North_American_1983 
> ",DATUM["D_North_American_1983",SPHEROID["GRS_1980", 
> 6378137.0,298.257222101]],PRIMEM["Greenwich",0.0],UNIT["Degree", 
> 0.0174532925199433]]
>
> I want to cut a rectangle with the following coordinates
>
> xmin –68.9125
> ymin 44.129
> xmax –63.0701
> ymax 48.3721
>
> from a shapefile with the following coordinates:
>
> xmin –69.35
> ymin 43.45
> xmax –50.85
> ymax 60.95
>
> The way I read it the smaller rectangle should lay totally within  
> the larger. So I have tried:
>
> ogr2ogr –spat –68.9125 44.129 –63.0701 48.3721 out.shp in.shp
>
> The does produce a new file, however, the metadata have not changed,  
> QGIS says it is the same as the original. In addition when I overlay  
> the out.shp over the in.shp, I do not have a smaller rectangle  
> within a larger. What I have is almost a diagonal swath retained  
> from the original file with two cookie cutter holes of contour lines  
> missing in the lower portion. The original shapefile contains  
> contour lines for temperature. The cookie cutter holes are areas  
> with closed polygons that are close to being spherical.
>
> What am I missing here? Does the spat option do something other than  
> clipping? Seemed straight forward but the results are strange.
>
> Thanks
>
> Alyre
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__________________________________________

    Paul Spencer
    Chief Technology Officer
    DM Solutions Group Inc
    http://www.dmsolutions.ca/