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| Subject: | RE: GISList: Compressed Terrain Data |
| Date: |
01/07/2003 11:20:56 AM |
| From: |
Neil Havermale |
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Cameron -
I think your Compressed Terrain Data (CTD) utility for cleaned-up USGS DEMs
has great merit. Your offer to support the increased "free" trade (by
easier access) via a shareware to "convert the (CTD)quads into an ascii
grid, x,y,z, tab, mif, mig or some other common format (but not back to
native DEM) for those who just want the raw data and do not need it in a
program" overcomes any attack of the anti-proprietaryists. It also seems to
overcome for me the emotive issue of trade based on public data. I like
your idea but please make certain the output has good metadata support -
MIF/MID seems very adequate but NOT SHP!
As you will quickly discover any really good idea attracts all sorts of "one
more feature" wish lists. I for one would suggest the following.
The USGS DEMed Quads are rather rude but very welcome. They provide the
basic terrain models many GISers seek although their bias and error within
landscapes of under a section are too coarse - but that's why we have
kinematic GPS? What I do like is that DEMs provide a de-facto organization
and standard of X:Y:Z data. Not all GIS X:Y:Z data is elevation nor is it
organized in quads. In fact, most of the really interesting spatial
analysis stuff are very abstract DEM-like surfaces. Its the stuff GIS value
is made from.
My long winded lead here is a "cleaned" DEM construct, or in your case,
CTDs, could have really great utility to the GISers who evolve past vector
mapping into spatial rasterizations of sight distance, sales sheds, distance
from anywhere to everywhere, and other thought provoking and consulting
profit spatial-isms.
So I think it would be really great if you published all of the USGS quads
in "your" CTD format which you allow to be freely converted into consistent
X:Y:Z text formats (with good metadata support) by your shareware or
freeware. I also like the idea of being able to DEM-ize abstract spatial
surfaces into consistent and efficient CDT format(s) as well. Please send
me your distribution terms and EULA ASAP!
So good luck and please stay in touch.
MidNight Mapper
aka neil
-----Original Message-----
From: Cameron Crum [mailto:c-crum@waveconceptsintl.com]
Sent: Friday, January 03, 2003 1:04 AM
To: gislist@geocomm.com
Subject: GISList: Compressed Terrain Data
This is a little off topic, but I'm trying to see if there would be an
interest in a very compressed (not zipped) form of elevation data. We
have come up with a technique for compressing DEM's that brings file
sizes down to about 127 KB per 1:24000 scale quad. To let you know, the
native USGS DEM's are over 1 MB each and the STDS archiving method in my
opinion is cumbersome to extract data from. We have also developed a DLL
and API that would allow programmers to access the data in these quads
programatically without having to decompress them, and we would offer a
free translator to convert the quads into an ascii grid, x,y,z, tab,
mif, mig or some other common format (but not back to native DEM) for
those who just want the raw data and do not need it in a program.
Additionally, the compression process detects and corrects the errors
inherent in many of the native USGS quads. So the end product is a
corrected quad at 1 tenth the original file size that doesn't require
3-4 steps to make it usable. Obviously, this is for the US only at the
moment, but the compression technique could be used on any data in the
world...we just don't happen to have access to that data. I'd be
interested to hear any questions or comments about this. Please Reply to
me directly so as not to clutter the list.
Thanks,
Cameron Crum
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