ppm output

[Mark Gregory]

Help, I cannot seem to figure out how GRASS decides how large to make the
output ppm file when using p.map with the ppm driver selected within p.select. 
 

At this point I am only using a raster file with 186 rows and 363 columns of 
data.  The scale value within the p.map commands does not seem to affect the 
size of the output ppm file.  Changing the region prior to running p.map does
affect the size of the output ppm file, but not in a logically (at least to me)
manner.

For example, when I use the entire raster file as input (186 rows, 363 cols.),
the size of the output ppm file is approx. 986k.  Next, when I use the same
data set (and cell size) but set the region to the first 93 rows and all 363
cols, the size of the output ppm file is 511k.  That makes sense.  HOWEVER,
when I use the same data set and cell size but set the region to the first 93
rows but only the first 180 columns of data, the output ppm file INCREASES to
1889k.  It this last case, the input data file was approximately 1/4 the size
(in terms of rows and columns of data), but the output ppm file was about twice
in size.  It does not make sense to me. 

In addition to adjusting the region and the p.map scale parameters, I have also
changed the GRASS_HEIGHT, GRASS_WIDTH, XDRIVER GRASS_HEIGHT and XDRIVER 
GRASS_WIDTH environmental variables without being able to affect the size of
the output ppm file.
 
Consequently, I would really appreciate any insight anyone could provide on
this matter.

Thanks in advance,


Mark


Mark Gregory                             mg at soil.agr.okstate.edu
Oklahoma State University                405-744-9603
Stillwater, OK 74078-6028                405-744-5269(fax)