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| GeoCommunity Mailing List |
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| Mailing List Archives |
| Subject: | RE: GISList: Compressed Terrain Data |
| Date: |
01/07/2003 11:20:55 AM |
| From: |
Dimitri Rotow |
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> 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
^^^
Perhaps you've been using cumbersome software. No reason you can't get an
SDTS DEM by simply doing a File - Open if your application is well crafted.
>
> 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.
IMHO, the last thing the world needs is yet another proprietary format in
which to store data, especially one that prevents users from converting to
the most common format used for such data. Why not propose an open format
using open algorithms for compression?
Also, as a practical matter, any high performance application will import
elevation data into whatever internal representation provides the highest
performance and greatest capability for that application. May as well use
already-existing, standardized formats for interchange.
> Additionally, the compression process detects and corrects the errors
> inherent in many of the native USGS quads. So the end product is a
Hmmm,... nothing like having the storage format make changes in a
standardized data set, no matter how sure of itself it may be.
> corrected quad at 1 tenth the original file size that doesn't require
> 3-4 steps to make it usable.
In exchange, it only requires users and vendors to agree to hand over to you
ownership of their ability to access what is now free data that is in the
public domain. If you own the format and you control the terms and
conditions of licensing the format you also ultimately control access to the
data published in that format.
If you provide a very "open" and inclusive SDK license like the ERMapper SDK
for their ECW compression you might find other applications willing to use
it. If it is as "closed" and paranoid as the MrSID SDK license you might
find yourself laying off half of your company as they did.
> 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.
>
I've replied to the list because I think the general proposition of
introducing yet another proprietary format is of general interest.
Cheers,
Dimitri
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