[postgis-users] ST_Difference lots of lines with lots of polygons

[Christy Nieman]

Hello,

I have been having difficulty figuring out how I might go about doing a 
difference of many lines and polygons.  For context, I have many (> 
3,000,000) contour lines that I want to difference based on many (> 
180,000) lakes.  My goal is to remove the sections of the lines that are 
within the polygons.  I know that I can use ST_Difference(aLine, 
aPolygon) to do this for one feature, but, what would the syntax look 
like to go though all my line and all my polygons and return just the 
lines/parts of lines that are outside of the polygons (and do this in as 
quickly and resource-friendly way as possible)?  The machine I am 
working on is a relatively well-powered desktop (quad core, 6GB RAM).

Thanks for any insight/suggestions,

Christy
-- 
Christy Nieman
GIS Technician
DM Solutions Group, Inc.
Email: cnieman at dmsolutions.ca
Web: http://dmsolutions.ca
Web: http://research.dmsolutions.ca