Opened 21 years ago
Last modified 21 years ago
#264 closed defect (fixed)
Documentation regarding SDTS DEM is incorrect
Reported by: | Owned by: | warmerdam | |
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Priority: | normal | Milestone: | |
Component: | default | Version: | unspecified |
Severity: | trivial | Keywords: | |
Cc: |
Description
The documentation found at the above URL states <i>USGS DEMs are always returned with a data type of signed sixteen bit integer."</i> SDTS DEMS can also be 32 bit floats, particularly in the case of decimeter DEMs. There is also rumor of centimeter DEMs, which will also employ 32 bit floats. The DDSH module will have a record denoting what binary type the ELEVATION field in the CEL module will be using.
Change History (2)
comment:2 by , 21 years ago
mcoletti@lychnobite.org wrote: >>I have corrected this. Can you point me to a "decimeter" DEM? Does this >>imply >>that an elevation of 1 meters is represented as 10 or just that the floating >>point values will vary by decimeter increments? > > > Try Kauai County, Koloa, HI 1:24k SDTS DEM. It has a "z resolution" of "0.1". > It has a file name of 1660083.dem.sdts.tar.gz. > > Try downloading it from: > > http://dl1.geocomm.com/download/6928/1660083.DEM.SDTS.TAR.GZ > > You should see elevation values like this: > > CVLS : Cell Values > ELEVATION : = 282.50000000 (FP32) > > CVLS : Cell Values > ELEVATION : = 283.10000610 (FP32) > > CVLS : Cell Values > ELEVATION : = 283.60000610 (FP32) > > CVLS : Cell Values > ELEVATION : = 284.20001221 (FP32) > > CVLS : Cell Values > ELEVATION : = 284.50000000 (FP32) > > CVLS : Cell Values > ELEVATION : = 284.89999390 (FP32) > > CVLS : Cell Values > ELEVATION : = 285.10000610 (FP32) > > Mind, the server is ver-r-r-r-ry slow. :'( Mark, The test file is already missing from dl1.geocomm.com. Anyways, I tried another old test file I have (abcdcatd.ddf, etc) and it reports floating point values with one decimal place of accuracy so it would appear that (as above) the decimeter datasets are simply measured in meters with one decimeter of accuracy. No problem. I will update the docs accordingly.
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