closed polygons from binary raster

[Michael Shapiro]

GRASS doesn't produce polygons. The vector structure is arc-node from
which polygons can be constructed (eg v.to.rast gets polygons from
the vector maps thru vector library calls to make raster maps using
polygon fill techniques), but they aren't stored explicitly as polygons.

If you want polygons then look at the code for v.to.rast to see what
calls it makes to prodcue polygons from the arc-node data stored in a vector
file.


|
|I have a binary raster map and want to produce from it a closed polygons
|bounding the clumps of non-zero cells.
|
|I run r.poly and, as its documentation states, it produces EDGES.  In practice
|this has meant that sometimes I get closed polygons (the first vertex repeated
|as the last one) and sometimes I get lines.  The resultant vector map is a
|mixture of polylines and polygons.
|
|Is there any other program available in GRASS that can reliably produce closed
|polygons, or is there some better way to pre-process my binary raster map
|so r.poly will?
|
|thank you.
|
|allan
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Michael Shapiro                        U.S. Army CERL                  
email:   shapiro at zorro.cecer.army.mil  Environmental Division          
phone:   (217) 352-6511  ext 526       P.O. Box 9005                   
fax:     (217) 373-7222                Champaign, Ill. 61826-9005
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