Details Ticket 2357


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Serial Number 2357
Subject Working with rasters in diverse resolutions
Area wish
Queue grass
Requestors gwurman@asu.edu
Owner none
Status open
Last User Contact Tue Mar 16 10:18:22 2004 (4 yr ago)
Current Priority 30
Final Priority 70
Due No date assigned
Last Action Tue Mar 16 10:18:22 2004 (4 yr ago)
Created Mon Mar 15 20:17:12 2004 (4 yr ago)

Transaction History Ticket 2357


Mon, Mar 15 2004 20:17:12    Request created by guest  
Subject: Working with rasters in diverse resolutions

Platform: other
grass obtained from: Trento Italy site
grass binary for platform: Downloaded precompiled Binaries
GRASS Version: 5.0.3

Hello,

I am working with multiple raster data sets in diverse resolutions, which presents
a problem.  For example, I cannot easily overlay a 1 meter-resolution USGS quad
on a 30 meter-resolution DEM.  To get all the data out of the quad I have to
oversample the DEM 900 times by setting the project resolution to 1m.

It seems to me that implementing support for multiple resolutions at once would
be a gargantuan pain for the poor programmers, but this is (imho) a serious limitation
of the program.  Is there a workaround that doesn't involve choking my RAM with
oversampled data?  Is there perhaps a workaround in NVIZ?

Thanks,
Gilead Wurman
ASU Active Tectonics
Mon, Mar 15 2004 22:15:50    Mail sent by morten@untamo.net  
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Date Mon, 15 Mar 2004 22:17:25 +0100 (CET)
From Morten Hulden <morten@untamo.net>
To Request Tracker <grass-bugs@intevation.de>
Cc grass5@grass.itc.it
Subject Re: [GRASS5] [bug #2357] (grass) Working with rasters in diverse resolutions
In-Reply-To <20040315191712.7D85713BC7@lists.intevation.de>
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On Mon, 15 Mar 2004, Request Tracker wrote:

> this bug's URL: http://intevation.de/rt/webrt?serial_num=2357
> -------------------------------------------------------------------------
> 
> Subject: Working with rasters in diverse resolutions
> 
> Platform: other
> grass obtained from: Trento Italy site
> grass binary for platform: Downloaded precompiled Binaries
> GRASS Version: 5.0.3
> 
> Hello,
> 
> I am working with multiple raster data sets in diverse resolutions, which presents
a problem.  For example, I cannot easily overlay a 1 meter-resolution USGS quad
on a 30 meter-resolution DEM.  To get all the data out of the quad I have to
oversample the DEM 900 times by setting the project resolution to 1m.
> 
> It seems to me that implementing support for multiple resolutions at once would
be a gargantuan pain for the poor programmers, but this is (imho) a serious limitation
of the program.  Is there a workaround that doesn't involve choking my RAM with
oversampled data?  Is there perhaps a workaround in NVIZ?
> 
> Thanks,
> Gilead Wurman
> ASU Active Tectonics

There is no need to oversample. Within a location you can create named 
regions which differ from the default region in resolution and/or 
geographic coverage.

If the resolution of your default region is 30m and you want to import a
1m map, then create a new 1m region and switch to that before importing.  
Or the other way around if your default is 1m.

The display driver will understand how to overlay maps with different 
resolutions.

Morten Hulden
  


Tue, Mar 16 2004 10:18:22    Mail sent by glynn.clements@virgin.net  
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From Glynn Clements <glynn.clements@virgin.net>
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Date Tue, 16 Mar 2004 09:12:16 +0000
To Morten Hulden <morten@untamo.net>
Cc Request Tracker <grass-bugs@intevation.de>, grass5@grass.itc.it
Subject Re: [GRASS5] [bug #2357] (grass) Working with rasters in diverse resolutions
In-Reply-To <Pine.LNX.4.44.0403152211300.1457-100000@htorp2.untamo.net>
References <20040315191712.7D85713BC7@lists.intevation.de> <Pine.LNX.4.44.0403152211300.1457-100000@htorp2.untamo.net>
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Morten Hulden wrote:

> > I am working with multiple raster data sets in diverse
> > resolutions, which presents a problem. For example, I cannot easily
> > overlay a 1 meter-resolution USGS quad on a 30 meter-resolution DEM. 
> > To get all the data out of the quad I have to oversample the DEM 900
> > times by setting the project resolution to 1m.
> > 
> > It seems to me that implementing support for multiple resolutions
> > at once would be a gargantuan pain for the poor programmers, but
> > this is (imho) a serious limitation of the program. Is there a
> > workaround that doesn't involve choking my RAM with oversampled
> > data? Is there perhaps a workaround in NVIZ?
> 
> There is no need to oversample. Within a location you can create named 
> regions which differ from the default region in resolution and/or 
> geographic coverage.
> 
> If the resolution of your default region is 30m and you want to import a
> 1m map, then create a new 1m region and switch to that before importing.  
> Or the other way around if your default is 1m.

The region settings are ignored when importing; maps are always
imported cell-for-cell (no resampling).

Resampling occurs when maps are read, or created by programs other
than importers.

> The display driver will understand how to overlay maps with different 
> resolutions.

The display drivers obtain their maps using the core libgis functions,
which will automatically resample them according to the current region
settings.

However, the issue here is that the poster has a low-resolution map
covering a relatively large region, and a much higher-resolution map
covering a small portion of that region.

Unfortunately, there isn't any way to display both simultaneously
without resampling both maps to the full region at the higher
resolution.

It wouldn't be a lot of work to provide a workaround for XDRIVER;
essentially, the display library would need to be changed to always
use the region settings from the WIND file, and not that stored on the
monitor. Then, you could do e.g.:

	d.erase
	g.region region=whole_area
	g.region res=30
	d.rast low_res_map
	g.region res=1
	d.rast -o high_res_map

This won't work at present, because the display library uses any
region settings which are stored on the monitor in preference to those
from the WIND file (which is why you often have to use d.erase after
changing the region).

OTOH, extending NVIZ is likely to be substantially more complex.

-- 
Glynn Clements <glynn.clements@virgin.net>


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