[GRASS5] [bug #3826] (grass) two r.resamp.rst issues

GRASS GIS GRASS GIS developer
1

this bug's URL: http://intevation.de/rt/webrt?serial_num=3826
-------------------------------------------------------------------------

Subject: two r.resamp.rst issues

If you run r.resamp.rst at a resolution other that that of the input map, the
output elev map is not created at the specified ew_res= and ns_res= resolution.
A warning is given that you are doing so, but it doesn't mention why that
might be bad. Interestingly the output map is actually written at the target
resolution, but it contains the data resolution from the original map. (target
was 50m, original was 100m)

If the input map is in another mapset (map@othermapset) then it gives an error
that the input map can't be found. (happens when it tries to copy the color
table I think) and exits with an error. (but processing is already done so
output map is ok, just without a colortable)

Hamish

ps - I've tidied up the module's code and strings a bit in CVS, so cvs update
before fixing...

-------------------------------------------- Managed by Request Tracker

2

Hamish,

We've run into that here too. One of my RA's did a test of interpolating to
a higher resolution using r.resamp.rst and the more complicated procedure of
generating a large number of points from a raster map, and then
interpolating from the points to a higher resolution.

r.resamp.rst is faster and more straightforward. BUT (a VERY big but), it
behaves exactly as you describe. It simply turns out a map that looks just
like the original map is subdivided into more grid cells, without any
interpolation. This makes the module essentially useless.

Michael
__________________________________________
Michael Barton, Professor of Anthropology
School of Human Evolution and Social Change
Arizona State University
Tempe, AZ 85287-2402

phone: 480-965-6213
fax: 480-965-7671
www: http://www.public.asu.edu/~cmbarton

From: Request Tracker <grass-bugs@intevation.de>
Reply-To: Request Tracker <grass-bugs@intevation.de>
Date: Sat, 12 Nov 2005 13:37:05 +0100 (CET)
To: <grass5@grass.itc.it>
Subject: [GRASS5] [bug #3826] (grass) two r.resamp.rst issues

this bug's URL: http://intevation.de/rt/webrt?serial_num=3826
-------------------------------------------------------------------------

Subject: two r.resamp.rst issues

If you run r.resamp.rst at a resolution other that that of the input map, the
output elev map is not created at the specified ew_res= and ns_res=
resolution.
A warning is given that you are doing so, but it doesn't mention why that
might be bad. Interestingly the output map is actually written at the target
resolution, but it contains the data resolution from the original map. (target
was 50m, original was 100m)

If the input map is in another mapset (map@othermapset) then it gives an error
that the input map can't be found. (happens when it tries to copy the color
table I think) and exits with an error. (but processing is already done so
output map is ok, just without a colortable)

Hamish

ps - I've tidied up the module's code and strings a bit in CVS, so cvs update
before fixing...

-------------------------------------------- Managed by Request Tracker

3

Michael Barton wrote:

Hamish,

We've run into that here too. One of my RA's did a test of interpolating to
a higher resolution using r.resamp.rst and the more complicated procedure of
generating a large number of points from a raster map, and then
interpolating from the points to a higher resolution.

r.resamp.rst is faster and more straightforward. BUT (a VERY big but), it
behaves exactly as you describe. It simply turns out a map that looks just
like the original map is subdivided into more grid cells, without any
interpolation. This makes the module essentially useless.

It's not useless because if you run the module at a resolution equal to the input raster map, the result is OK.
The warning message should be replaced by a fatal error that exits the command.

Jaro

Michael
__________________________________________
Michael Barton, Professor of Anthropology
School of Human Evolution and Social Change
Arizona State University
Tempe, AZ 85287-2402

phone: 480-965-6213
fax: 480-965-7671
www: http://www.public.asu.edu/~cmbarton

From: Request Tracker <grass-bugs@intevation.de>
Reply-To: Request Tracker <grass-bugs@intevation.de>
Date: Sat, 12 Nov 2005 13:37:05 +0100 (CET)
To: <grass5@grass.itc.it>
Subject: [GRASS5] [bug #3826] (grass) two r.resamp.rst issues

this bug's URL: http://intevation.de/rt/webrt?serial_num=3826
-------------------------------------------------------------------------

Subject: two r.resamp.rst issues

If you run r.resamp.rst at a resolution other that that of the input map, the
output elev map is not created at the specified ew_res= and ns_res=
resolution.
A warning is given that you are doing so, but it doesn't mention why that
might be bad. Interestingly the output map is actually written at the target
resolution, but it contains the data resolution from the original map. (target
was 50m, original was 100m)

If the input map is in another mapset (map@othermapset) then it gives an error
that the input map can't be found. (happens when it tries to copy the color
table I think) and exits with an error. (but processing is already done so
output map is ok, just without a colortable)

Hamish

ps - I've tidied up the module's code and strings a bit in CVS, so cvs update
before fixing...

-------------------------------------------- Managed by Request Tracker

_______________________________________________
grass5 mailing list
grass5@grass.itc.it
http://grass.itc.it/mailman/listinfo/grass5

4

Perhaps we misunderstand each other, or maybe it works for you.

The whole point of the module is to change the resolution of the raster map.
In my recent experience (I've tried it on a Mac and on Fedora Core 4), this
doesn't seem to work, regardless of the region settings when you run the
module. It changes the resolution, but it seems to have the effect of simply
making more grid cells without correctly interpolating between them. For
example, going from a 30m resolution DEM to a 15m resolution using
r.resamp.rst seems to produce 4 15m cells within the area of an original 30m
cell, but each of the 15m cells has the same resolution as the original
cell. This is not how it should work.

Michael
__________________________________________
Michael Barton, Professor of Anthropology
School of Human Evolution and Social Change
Arizona State University
Tempe, AZ 85287-2402

phone: 480-965-6213
fax: 480-965-7671
www: http://www.public.asu.edu/~cmbarton

From: Jaro Hofierka <hofierka@geomodel.sk>
Date: Sun, 13 Nov 2005 23:20:06 +0100
To: Michael Barton <michael.barton@asu.edu>
Cc: <grass5@grass.itc.it>, Helena Mitasova <hmitaso@unity.ncsu.edu>
Subject: Re: [GRASS5] [bug #3826] (grass) two r.resamp.rst issues

Michael Barton wrote:

Hamish,

We've run into that here too. One of my RA's did a test of interpolating to
a higher resolution using r.resamp.rst and the more complicated procedure of
generating a large number of points from a raster map, and then
interpolating from the points to a higher resolution.

r.resamp.rst is faster and more straightforward. BUT (a VERY big but), it
behaves exactly as you describe. It simply turns out a map that looks just
like the original map is subdivided into more grid cells, without any
interpolation. This makes the module essentially useless.

It's not useless because if you run the module at a resolution equal to
the input raster map, the result is OK.
The warning message should be replaced by a fatal error that exits the
command.

Jaro

Michael
__________________________________________
Michael Barton, Professor of Anthropology
School of Human Evolution and Social Change
Arizona State University
Tempe, AZ 85287-2402

phone: 480-965-6213
fax: 480-965-7671
www: http://www.public.asu.edu/~cmbarton

From: Request Tracker <grass-bugs@intevation.de>
Reply-To: Request Tracker <grass-bugs@intevation.de>
Date: Sat, 12 Nov 2005 13:37:05 +0100 (CET)
To: <grass5@grass.itc.it>
Subject: [GRASS5] [bug #3826] (grass) two r.resamp.rst issues

this bug's URL: http://intevation.de/rt/webrt?serial_num=3826
-------------------------------------------------------------------------

Subject: two r.resamp.rst issues

If you run r.resamp.rst at a resolution other that that of the input map,
the
output elev map is not created at the specified ew_res= and ns_res=
resolution.
A warning is given that you are doing so, but it doesn't mention why that
might be bad. Interestingly the output map is actually written at the target
resolution, but it contains the data resolution from the original map.
(target
was 50m, original was 100m)

If the input map is in another mapset (map@othermapset) then it gives an
error
that the input map can't be found. (happens when it tries to copy the color
table I think) and exits with an error. (but processing is already done so
output map is ok, just without a colortable)

Hamish

ps - I've tidied up the module's code and strings a bit in CVS, so cvs
update
before fixing...

-------------------------------------------- Managed by Request Tracker

_______________________________________________
grass5 mailing list
grass5@grass.itc.it
http://grass.itc.it/mailman/listinfo/grass5

5

Perhaps we misunderstand each other, or maybe it works for you.

The whole point of the module is to change the resolution of the
raster map. In my recent experience (I've tried it on a Mac and on
Fedora Core 4), this doesn't seem to work, regardless of the region
settings when you run the module. It changes the resolution, but it
seems to have the effect of simply making more grid cells without
correctly interpolating between them. For example, going from a 30m
resolution DEM to a 15m resolution using r.resamp.rst seems to produce
4 15m cells within the area of an original 30m cell, but each of the
15m cells has the same resolution as the original cell. This is not
how it should work.

The current region resolution needs to match the input map's resolution,
then it should work. Could you try the latest cvs version and see if you
can replicate the error?

Hamish