Hey all,
I have a couple questions about VPB. I've been playing around with it
for about a month now, and have reached as far as I can go. After some
help from here a month ago (thanks all) I spent some time digging
through the source code to see what I could find and have reached about
as far as I can go by myself. It appears that I am trying to do
something that VPB does not support yet. I was hoping I could find a
simple change to do what I want, but it doesn't appear to be that easy.
Or at least, my mind couldn't get around the code enough to figure it
out. Anyway, here are my questions/concerns:
1) I am trying to do a model of the Moon. I have data in PDS format
that reads into GDAL just fine. I can run osgdem -l 1 -d foo.pds -o
bar.ive and it works fine. If I peek at the resulting ive file, I can
see it has a CoordinateSystemNode at the top with the right WKT in it.
There is no Ellipsoid because the terrain is flat. And a quick look at
the vertices seem to put them in the right area (uses moon radius, not
Earth radius). But I really need to do a spherical model of the Moon,
since I am doing Lander simulations and things like that matter. The
only way I know to make a spherical terrain is to use the "--geocentric"
command. After tracing all over the code, it appears that this forces
VPB to use the WGS84 coordinate system, no matter what else I try. When
the intermediate and destination coordinate systems are created, it
automatically creates the default WGS84 coordinate system with
appropriate Ellipsoids, no matter what the input data is. So no matter
how I try, I always get an Earth-like Ellipsoid with WGS84 coordinate
system in my output. Am I doing something wrong? Is there a
command-line to indicate what I want the final coordinate system to be?
I have a WKT for the moon. Is there a way to force that? I tried
entering that WKT in, but it was never used for creating the
intermediate and destination data sets.
2) My data is in a Polar Stereographic projection, rather than a
cylindrical type projection. Which means that the center of the image
is the North (or South) Pole. Lat lines radially extend from the center
and Lon-lines are concentric rings around the center. When I use this
on for a "--geocentric" data set, it shows up as a partial "wedge" or
"orange slice" from the north pole to about 75 degrees North. It
appears to me that it is being treated like a cylindrical projection. I
have not looked into this problem as much. Is this a GDAL issue? Where
does the projection from a given pixel to a Lat-Lon happen?
Anyway, thanks for the help. VPB is a pretty amazing piece of software.
I've been able to do huge datasets quickly and easily, so I'm really
excited to get it working on the Moon too. I appreciate any help.
Paul Brewster
Data Visualization and Analysis Lab
NASA Langley Research Center
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