Dylan Beaudette wrote:
On Tuesday 19 December 2006 08:24, Yu Zhang wrote:
I wonder if anyone can provide a reference to the
algorithm used in v.to.rast. I found mismatches
between GRASS raster with Arcview one that were
derived from the same polygon layer. v.to.rast in
GRASS tends to underestimate the number of cells
within certain polygons
Do you have some images which demonstrate the comparison ?
Hi,
Sorry for jumping in, but it might be related.
I don't know for polygons, but I have similar experience with lines -
not enough cells are rasterised compared to what you would expect -
line's start and end happen to be skipped. Not mentioning that
v.to.rast tries to kindoff approximate the line's shape than to detect
which cells the line actually goes through.
See bug report:
http://intevation.de/rt/webrt?serial_num=4488
The examples mentioned:
http://www.nabble.com/attachment/4566255/0/wrong_cell2.png
http://www.nabble.com/attachment/4566255/2/wrong_cell4.png
http://www.nabble.com/attachment/4566255/1/wrong_cell3.png
http://www.biol.uni.wroc.pl/sieczka/udostepnione/grass/vtorast/wrong_cell.png
r.thin doesn't help:
http://www.biol.uni.wroc.pl/sieczka/udostepnione/grass/vtorast/rthindoesnthelp.png
BTW, two other long standing v.to.rast bugs:
http://intevation.de/rt/webrt?serial_num=5163
(solution by Glynn is there, can someone apply it please?)
http://intevation.de/rt/webrt?serial_num=4480
Maciek