[GRASS-user] Using r.buffer on image with geographic coordinates

Ned Horning horning at amnh.org
Fri Mar 25 09:42:54 EDT 2011

Hi - I am trying to create buffers for large (~1GB) line and polygon 
vector files. I tried v.buffer but after letting it run overnight with 
no apparent progress I killed the process. I'm not aware of any software 
capable of buffering large vector files on a modest computer so that 
wasn't a big surprise. I then converted the vector to a large (23GB) 
raster file and am now trying r.buffer. I ran some tests on small images 
but can't figure out how the distance parameter works when an image has 
latitude/longitude coordinates. My image is in a geographic 
(latitude/longitude) projection with a resolution of 0.00025 (~27.75m) 
and I'd like to create a buffer with a distance of 0.0018 (~200m). How 
to I do that without projecting my image? I'm using GRASS 7.0 on 64 bit 
Ubuntu 10.04.

The manual seems to indicate that I can choose the distance units so I 
tried distances=200.0 and units=meters but that converted the entire 
image to a buffer so the distance was clearly too large. I then tried 
distances =0.0018 (the manual states that r.buffer uses "ellipsoidal 
geodesic distance measure for latitude/longitude locations) and 
units=meters but that didn't create any buffer. My last test was to use 
the number of pixels to define the distance so I tried distances =7.2 
and units=meters and that created a buffer roughly one pixel wide.

Any thoughts on how to buffer a large vector or raster data set would be 

All the best,


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