[GRASS5] Outstanding issues for the 5.0 stable release
Eric G. Miller
egm2 at jps.net
Thu Jun 27 22:35:31 EDT 2002
On Fri, Jun 28, 2002 at 02:53:59AM +0100, Glynn Clements wrote:
> 1. This seems self-contradictory. For most GRASS raster commands, the
> size of the output map is determined from the current region settings,
> regardless of the portion which will be non-null.
Errm. I was mixed up... I never use r.proj due to its memory
requirements so was remembering it as being run from the input mapset.
Therefore, it's seems like it should be treated like an import/export
routine since it's run in the target location.
The problem I think most folks run into is setting the current region
for the projection but not having a good idea what it should be set at.
So, as a user, do I have to project some points or a vector box first
just to guess what the current region extents should be? Maybe the
behavior is what some users want, but I'd bank that in general users
would want to project the entire input at its data resolution into the
current mapset (much like any raster import). If I want/need to cut it
down or reduce the resolution, I'd make those modifications before or
after the projection (depending on what I'm using to make those
> 2. Bear in mind that r.proj "works backwards". For each output cell,
> it projects that cell's coordinates via the inverse projection
> function to obtain the corresponding coordinates in the input map, and
> copies the corresponding cell value from the input map to the output
> map. Forward projection is only used to compute an optimal bounding
As a user, I don't care how it works internally ;-)
> 4. When I say "computes", "guesses" may be a better term, as the
> computation is fallible. It assumes that the boundary of the
> projections of the cells is the projection of the boundary of the
> cells. While this is likely to hold true for "almost affine"
> transformations (i.e. projecting "small" regions), it can fail,
> particuarly for creating "whole earth" maps from a lat-long source.
Yea, a bit tricky there...
Eric G. Miller <egm2 at jps.net>
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