Hi, Thanks for that, I seem to have something working now (or so I think), my shape file is the contours lines for a reasonably hilly area (100Mb), and I'm clipping it to an area of about 1/12. The only thing is it's still running about 17 hours later. Is v.overlay slow or have I done something wrong, here are my steps:
g.region vect=NZMG_s27 v.in.region output=cutter type=line --overwrite v.overlay ainput=wellington_contours atype=line binput=cutter output=clipped operator=and Thanks in advance Matthew On Thu, Sep 4, 2008 at 9:09 PM, Craig Leat <[EMAIL PROTECTED]> wrote: > Hi Matthew > > Matthew Huck wrote: > > Hi, I've got a reasonably large shapefile that I wish to break down > > into areas that match the topographic maps in NZMG. I've got a python > > script that creates a shapefile with each topomap as a polygon in it > > (and I can create a shapefile per topo map too if required). What I > > can't work out how to do is to clip my master shapefile by the smaller > > shapefiles. I've seen ideas of copying across the features if they > > intersect with the clipping box, but the data is contour lines so I > > want to "cut" the contour lines at the boundry of the clipping boxes. > > Any ideas on the best way to do it, I can get MapWindow to do it > > (sometimes, but it crashes frequently). > > I use GRASS for this sort of task. The basic steps are: > > 1. Import shape files using v.in.ogr > 2. Set the region extents (a bounding box for the area of interest) > using g.region > 3. Make a vector to be used as a cutter - v.in.region > 4. Select within the region box and cut on the boundary using v.overlay > > It's quite easy to roll these steps into a script and is definitely > the way to go if you have to do this many times. > > Craig > > gdal/ogr devs, an ogr2tiles.py would be quite nice. >
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