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| GeoCommunity Mailing List |
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| Mailing List Archives |
| Subject: | GISList: SUM: 3D Generation |
| Date: |
06/25/2002 04:38:46 AM |
| From: |
DeepakKa .. riskinc.com |
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Hi
I'm summing up the query I had posted at MI user List and GisList
about 3d Generation.
I got a tremendous response for the same, which I have produced after these
comments.
I went for Vterrain's VTP.
Some other links and resources that I explored and would like to share
across are...
DEM Terrain Visualization and Flyby animation. Though into 14the release,
you can't get it free download.
Its a good tool.
Link http://www.terrainmap.com/rm13.html (3DEM 7.0 ver)
http://www.simtel.net/pub/pd/6700.shtml (3DEM 7.0 ver)
These URL's have lot of info/ material/ links to explore
http://www.terrainmap.com
http://www.remotesensing.org
http://www.redhensystems.com
http://www.innovativegis.com
http://tahoe.usgs.gov/DEM.html
http://www.geovrml.com
Response received
****************************************************************************
Mike Faries
www.cadeasy.com
http://www.scisoftware.com/products/gwn_dtm_overview/gwn_dtm_overview.html
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Tom Citriniti
You may want to take a look at the Visualization Toolkit (Vtk) which was
developed by some ex-GE R&D people. You can find it at:
http://www.kitware.com
It has all the things you are looking for, IDW, TIN, DEM reader, Texture
mapping (draping), and VRML support.
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Chris Nunno
http://www.itspatial.com/ITspatial_CoreCompetencies.html
Look at: Terrain/Urban Database Development
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Jakob Lanstorp
You might want to try OpenGL.
http://www.sulaco.co.za/opengl4.htm
http://nehe.gamedev.net/
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Frank Warmerdam
I would encourage you to look at the VTP software at:
http://www.vterrain.org/
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Eric Maranne
Beyond the final rendering lib used (OpenGL or DirectX or whatever), the
most discriminant thing is the projected use.
To be more precise :
if you want to use your data for creating a 3D surface using IDW (theory is
widely known and used, and algorithm is straightforward, google will help
you without problem), I don't understand why you'd need a TIN, unless you
want to perform a very complex data mix from interpolation of scattered
points and mesh data.
You may use a TIN (search for Delaunay triangulation), if your point data
is
defining very accurately the surface to be constructed (like points from
contour lines). Building a TIN straight from your point data will create a
surface honorring all points, without under/overshoots nor any smoothing.
Beware, this doesn't mean that there can't be any smoothing at rendering
time: you may alter crease angle, derive a spline surface from the TIN or
use it to create local BezierPatches for example. But the surface
description itself will be fitting your point set.
You may use IDW if you want a surface that *approximates* a best fit of
your
point set. You won't have any under/overshoot, but your surface will be
very
smoothed in the end, and the process is very mainly used to produce a DEM
(a
matrix of points), though nothing prevents you to qualify a set of
scattered
points using IDW, though I can't see the reason why one should do this.
Other algorithms can be used to build an approximation of the surface :
gridding, fifth order interpolation, etc ... each of these won't ensure
agains under or over shoots, but you may choose wether you allow over *or*
undershoots, depending on your needs. for example : for submarine
navigation
you'd prefer allowing overshoots rather than undershoots ... while a
smoothed IDW surface is of no use ... while a atmospheric inversion surface
would be better represented smoothed by an IDW ...
So, the algorithm used for surface reconstruction depends on the quality of
your pointset, the data represented, and the projected use of the surface.
Now, more generally speaking, from a representation standpoint. You may
have
understood that the data can be described as a TIN or a mesh. A mesh will
always be smoother than a TIN. May be good, may be bad ... depends. For
example, you'll never be able to represent a vertical cliff or a flat lake
or road using a mesh, no matter the points spacing.
Next, what do you need to use to transmit your surface representation, I
mean as a medium ? If you want to publish it thru any small Internet
wiring,
a DEM is usually more concise (lightweight) than a TIN. If this is an
urgent
point then this may decide.
But beware, if you want to represent almost vertical surfaces precisely
(cliffs, houses ...) then you need a very small spacing for the points of
a
mesh ... so a very big footprint ... much much bigger than what you could
ach
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