LtPlus and DEM generation

Mark S. Gregory mg at
Mon Aug 16 10:31:01 EDT 1993


I am interested in talking with anyone who has experience with LtPlus and the
generation of DEM data.

Some time ago, we obtained from CERL the LtPlus version which has been ported
to the SUN platform.  We are using the software to clean and attribute scanned
images of topographic contours for 1:24000 scale USGS maps.  Our goal is to
generate USGS DEMs.  Everything seems to work great except for one critical 
problem.  After we clean and attribute the resulting vector contours, we attempt
to generate the DEM by exporting the data in the LtPlus dem format.  The form
and size of the resulting data set is comparable the DEM data sets of other
7.5 minute quads previously obtained from USGS.  Unfortunately, the exported
data set has maximum and minimum elevation values which are 'out of range' of
any possible value.  For example, approximately 1/3 of the generated data 
values appear to be reasonable (300-400 meters) for the area over which the 
data covers.  At the same time, about 2/3 of the data have values which range
from -0.9D+09 to 1.2D+10.

We have exported the vector in other formats (such as DXF) and input the
resulting file into GRASS.  We run of these vectors and get a raster
data set which appears correct.  Unfortunately, we need the data in USGS DEM
format and not GRASS raster format.  

Our problem, therefore appears to be in the manner in which we are attempting 
to use the DEM export option in LtPlus, or the DEM export option in LtPlus is
not properly working in the SUN version obtained from CERL.

I would greatly appreciate correspondence with anyone who has had experience
with LtPlus (the pc or the SUN version) or anyone who might have some ideas on
this problem.

Thanks in advance,

Mark Gregory                              mg at
Oklahoma State University                 (405) 744-6417
Stillwater, OK  74078                     (405) 744-5269 fax

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