[GRASS-user] Change detection in a Vector (polyline) dataset

[Moritz Lennert]

On 19/03/08 04:18, Andrew Schroeder wrote:
> Hi Everyone,
> 
> Can you tell me if GRASS is able to detect change between two input 
> polyline shapefiles?  I have a 5m contour set for two different years at 
> a particular mine, and I'm looking for a way to automate detection of 
> the yearly pit advances.
> 
> Basically, I'm looking for something to subtract file A from file B 
> (b-a=change) and output a file showing just the lines that changed 
> between the two files.
> 
> Thanks for any direction you can offer.

IIUC, this would be a classic example of v.overlay usage, only that 
v.overlay does not support two line maps (i.e. not line + line, only 
area + point/line/area). I don't really know why this is so.

If your contours are closed you could transform them into areas and then 
run v.overlay with operator=not.

Moritz