[Gdal-dev] GDAL data model, caching, GDALProjDef

Derrick J Brashear shadow at dementia.org
Sun Feb 16 15:07:27 EST 2003

On Sun, 16 Feb 2003, Ed McNierney wrote:

> Derrick -
> I have some relevant experience, having collar-clipped over 60,000 USGS
> quads <g>.  There are a few commercial tools out there that will do it


> Both are, I think, Windows-only apps.

Hmm. Being both commercial and non-Linux make them "right out". This is
basically a hobby venture, no hope or intent of ever generating money.

> Clipping the collars is trickier than it might appear.  I'm not sure
> what you mean by "the problem with images that fall at the center of the
> UTM zone" is, but the Blue Marble tools have a long-reported and unfixed
> bug with those quads (they clip to the bounding rectangle formed by the
> projected four corners of the ROI, which clips off the middle of
> southern edge of the DRG).  You also need to remember that the datum of

That's in fact the sort of problem I meant.

> the latitude / longitude bounding box for the DRG may NOT be the same as
> the datum of the DRG itself.  The USGS, TVA, and Teale metadata that
> describes the bounding box is also often quite buggy, so you need to
> check your results carefully.

Sure, but again, it's a "hobby-use" project, so close enough will suffice.
For that matter, if I wanted to abstract code, Xastir (which builds on
most unix systems, can display geotiffs, but isn't gdal-aware yet either)
does on-the-fly clipping of collars down to the map neatline based on the
metadata, in fact yielding a "close enough" except for the fact that it
does this for display and not to write the maps back out.

> If you don't care about the tools, but simply want to produce some
> collar-clipped USGS DRGs, I've got plenty.  Contact me off-list and I'll
> see if we can help.

Pennsylvania distributes collar-clipped 1:24k (at least) DRGs, and I have
a set of those to play with. Once I get beyond this area into Ohio or West
Virginia I need to generate some myself, so this is really all about my
hope for a tool. 

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