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
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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
achieve with a TIN.
If you decided what representation you want, then for the draping. ...
There's no real difference in draping a mesh or a TIN. What is needed is to
define for each point (of a mesh or a TIN) a correponding point in the
raster, usually expressed as a percentage of u,v raster coordinates (a bit
like MI is doing ... but, cleverly, 3D Engines are twisting the raster and
*not* the vector !, MI is the only tool I know persisting in nonsense, but
that's another rant). However, if you use orthorectified images, then the
process is straightforward.
Most important for the draping : the raster size. Beyond the obvious
download weight, any rendering engine will accept raster only up to some
size (directX or openGL). If the size is too big, the raster is scaled down
automatically. A good advice is to never go beyond 1024*1024 pixels.
This is very important, because this may mean tiling your geometry to fit
small raster tiles... And this is *the* point : it's very easy to slice a
mesh geometry ... and much harder to slice a TIN geometry...
The final step is the rendering engine. The easiest one .... I, for myself,
do prefer using VRML. VRML ensures a widespread display ability thru
systems, OSes, an easy Internet capability, and a vendor independance. Note
that the same VRML engine may be used on top of DirectX or OpenGL. It
provides a higher level abstraction layer. Of course, one more layer causes
less framerate, but the advantages are sooo big. AMAF, I achieve more than
30 fps on a 1000 square km TIN ground draped with 50 cm/pixel orthoimagery
(more than 300 000 triangles on 500 square meters tiles) on a standard
machine (well, almost ... Pentium 2GHz, Win XP, GEForce4 126 Megs). Do you
need more ? ... So the renderer choice isn't the point.
Usefull (very) link : www.geovrml.org look for Chris Thorne slicers, use
Cortona for display (has got a native c++ GeoVRML implementation) or if
you're a JAVA fanatic (I'm not) use standard java libraries.
If you want to keep it KISS, look in the MI-L archives for DEM and VRML, I
posted two years or so an example for creating a DEM representation in VRML
using MI and Notepad...
Hope have been clear enough... :/ 3D is a bit complex to explain at
midnight
BTW, for those interested, watch my site (www.geovrml.com) in the coming
month, I hopefully, find some time for presenting my latest project : a
virtual forest fire fighting, collaborative and immersive training tool.
Very impressive screenshots.
****************************************************************************
Doris Griessnig
Thanks for your mail. I've looked at the adresses you've sent me and think
they are quite interesting, above all the TinLib at vterrain.org.
I did an investigation of global data sources and tested a couple of
programmes, demo versions as well as freegis
(www.freegis.org/index.en.html). Among others:
Geotrans (including source code in C) an application program which allows
users to easily convert geographic coordinates among a wide variety of
coordinate systems, map projections, and datums.
http://164.214.2.59/GandG/geotrans/geotrans.html
TNTlite, a GIS and image processing software including a demodataset and a
very useful manual (my favourite, although it takes getting used to). It's
not a demo version, but a full working system that is limited only in the
size of the project materials it handels.
www.microimages.com/tntlite
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