Reclass problem

Michael_Hanratty · April 1, 1997, 4:52pm

Fellow GRASS user,

I have the following raster file that I'd like to reclassify.

Mapset <washita> in Location <utm14>
GRASS 4.1 > r.cats map=lulc
Reading lulc in washita ... 100%
0 no data
11 urbn
12 urbn
13 urbn
14 urbn
16 urbn
17 urbn
21 past:swht:hay
24 agrl
31 rnge
32 rngb
33 rnge
41 frsd
43 frst
53 watr
75
76

What I would like to do is to split the areas with category 21 (past:swht:hay)
into three categories of equal area. For example, if category 21 covers 30
sq.km., I'd like to divide that area in any manner that is convenient so that I
have 10 sq.km. of area with category past, 10 sq.km of area with category swht,
and 10 sq.km. of area with category hay.

Does anyone have a suggestion for how to do this? I'd like a procedure that I
can automate so that I can apply it to a number of masked regions within a
raster layer.

Thanks.
Mike

Michael Hanratty Phone: (612) 627-4590
St. Anthony Falls Laboratory Fax: (612) 627-4609
Dept. of Civil Engineering
University of Minnesota
Mississippi River @ 3rd Ave. SE
Minneapolis, MN 55414

Malcolm_Williamson · April 1, 1997, 8:28pm

On Tue, 1 Apr 1997, Michael Hanratty wrote:

Fellow GRASS user,

I have the following raster file that I'd like to reclassify.

Mapset <washita> in Location <utm14>
GRASS 4.1 > r.cats map=lulc
Reading lulc in washita ... 100%
0 no data
11 urbn
12 urbn
13 urbn
14 urbn
16 urbn
17 urbn
21 past:swht:hay
24 agrl
31 rnge
32 rngb
33 rnge
41 frsd
43 frst
53 watr
75
76

What I would like to do is to split the areas with category 21 (past:swht:hay)
into three categories of equal area. For example, if category 21 covers 30
sq.km., I'd like to divide that area in any manner that is convenient so that I
have 10 sq.km. of area with category past, 10 sq.km of area with category swht,
and 10 sq.km. of area with category hay.

Does anyone have a suggestion for how to do this? I'd like a procedure that I
can automate so that I can apply it to a number of masked regions within a
raster layer.

Do you care if the areas are randomly intermixed? If not, use r.random.
You can apply a mask, generate a new random layer consisting of 33% of
the area, generate a new mask to include those cells, generate a new
random layer consisting of 50% of the now available area, and finally use
r.mapcalc to make a new layer consisting of the remainder (and then put
them back together). It may not be pretty, but I believe that it would work.
--
Malcolm D. Williamson - GIS Specialist E-mail: malcolm@cast.uark.edu
Center for Advanced Spatial Technologies Telephone: (501) 575-6159
Ozark Rm. 12 Fax: (501) 575-5218
University of Arkansas
Fayetteville, AR 72701

Thanks.
Mike

Michael Hanratty Phone: (612) 627-4590
St. Anthony Falls Laboratory Fax: (612) 627-4609
Dept. of Civil Engineering
University of Minnesota
Mississippi River @ 3rd Ave. SE
Minneapolis, MN 55414

Angus_Carr1 · April 1, 1997, 11:34pm

Use a random number generator to generate a random map (using head -6 to
trim the top header section of an existing map coming out of r.out.ascii
and then catting them together) of values from one to three. Use an
r.mapcalc statement to create the result map
for example, assuming a 3 x 3 map, and bash shell:

r.out.ascii oldmap | head -6 > randmap
for augh in 1 2 3 4 5 6 7 8 9 ; do random 1 3 >> randmap ; done
r.in.ascii i=randmap o=random_now_in_grass
r.mapcalc "redone=if(oldmap==21,120+randmap,oldmap)"

The product is the contents of oldmap where oldmap != 21 , else 121-123
(the three new classes).

The program random is:

================
#include <stdio.h>
#include <stdlib.h>
#ifndef RAND_MAX
#define RAND_MAX 2147483647
#endif

void main(int argc,char *argv)
{
int top,bottom,range;
top=atoi(argv[2]);
bottom=atoi(argv[1]);
range=top-bottom;
if (range < 0) range = 0-range;
printf("%d ",(int) ((rand() / RAND_MAX * range ) + bottom ) );
}

This program (completely untested) will read a pair of numbers from the
command line and spit out a random number between the two (inclusive).
You could, of course, write an analagous GRASS program. It wouldn't be
hard.

Good luck. If it doesn't work, have a few kicks at it then give me a call.

Angus Carr,
Masters of Forestry student

On Tue, 1 Apr 1997, Michael Hanratty wrote:

Fellow GRASS user,

I have the following raster file that I'd like to reclassify.

Mapset <washita> in Location <utm14>
GRASS 4.1 > r.cats map=lulc
Reading lulc in washita ... 100%
0 no data
11 urbn
12 urbn
13 urbn
14 urbn
16 urbn
17 urbn
21 past:swht:hay
24 agrl
31 rnge
32 rngb
33 rnge
41 frsd
43 frst
53 watr
75
76

What I would like to do is to split the areas with category 21 (past:swht:hay)
into three categories of equal area. For example, if category 21 covers 30
sq.km., I'd like to divide that area in any manner that is convenient so that I
have 10 sq.km. of area with category past, 10 sq.km of area with category swht,
and 10 sq.km. of area with category hay.

Does anyone have a suggestion for how to do this? I'd like a procedure that I
can automate so that I can apply it to a number of masked regions within a
raster layer.

Thanks.
Mike

Michael Hanratty Phone: (612) 627-4590
St. Anthony Falls Laboratory Fax: (612) 627-4609
Dept. of Civil Engineering
University of Minnesota
Mississippi River @ 3rd Ave. SE
Minneapolis, MN 55414