[GRASS-user] UTM concepts

Brent Wood b.wood at niwa.co.nz
Sun Oct 8 21:53:58 EDT 2006

>> Hi,
>> I'm trying to learn GRASS a second time and find myself struggling again
>> with the basic issue of defining a region.
>> I have a series of data sources with varying projections and extents
>> covering the region I'm interested in.  I would like to work on a UTM
>> projection with WGS84 datum for all analyses of this region, so would have
>> to reproject and clip the original data sources to this standard.
>> Since the region of interest covers several UTM zones, I don't understand
>> how I should define the region for this project.  For instance, If I
>> choose the UTM zone corresponding to the center of the region I'm
>> interested in, how does one specify the limits of the region, considering
>> that the data will span several (4) UTM zones?

This addresses my main (pretty much only!) gripe about GRASS. I suggest 
that projections, etc are simply metadata describing a dataset. As such, 
being forced to change all my data to one predefined projection/datum is 
a significant inconvenience, which has largely precluded my making any 
real use of GRASS.

I get data & updates from various institutes/repositories around the 
world, in a variety of projections. I want to use these data as they 
are, without requiring two complete sets (the GRASS reprojected copy & 
the original) which requires on the fly reprojection.

GMT, QGIS, PostGIS and increasingly, UMN mapserver (the FOSS GIS tools I 
use most) all support on the fly reprojection, so my workspace can 
pretty much seamlessly overlay data stored in NZTM, NZMG, mercator, UTM, 
lat/long and polar coordinate systems & projections.

Is there any plan to make GRASS less restrictive in the way it deals 
with data covering the same region but in different projections? (Or 
have I missed something & it has already been done?)

I assume the entire GRASS codebase is oriented around the 
mapset/predefined region/datum/projection and that any shift from this 
model would be a huge undertaking, but am wondering if supporting on the 
fly reprojection has been considered at all?


   Brent Wood

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