From: aearl@afit.af.mil (Arthur J. Earl)
Subject: Ray tracing and imagery enhanced terrain modeling
Originator: aearl@scgraph
Keywords: photogrammetry, ray tracing, terrain modeling, computer graphics.
Organization: Air Force Institute of Technology
Date: Tue, 10 Nov 1992 18:16:49 GMT

Problem:
I now what to map images on to a terrain model.  Are there any puplic 
domain programs or references on performing ray tracing on to 3d surfaces?  
Has anyone else approached a similar problem.  (aearl@afit.af.mil)

+ <- Video System Platform(One lens not a stereo system)
 .  .
   .   .       .
     .    .   .
       .     . <- Image Plane 
         .  .   .
           .       .
          .  .        .
         .     .         .
                 .          .
                   .           . 
                     .             .
                       .              .
                         .               .
--------------------------________________--------   <-Earth's Surface.
                         A       ^        B
                                 |
                           Real World Terrain*
                          (trapazoidal in shape)

                                      /|
                                     / |
               Overhead view of     |  |
               Trapazoid:           |  | 
                                   A \ |
                                      \|
                                        B


Purpose:  During Desert Storm I was in charge of an ad hoc cell that analyzed
imagery for the Commander of the 1st Infantry Division.  There was a time lag 
in acquiring mosaic photos of the battlefield.  However, we received video tapes
quickly.  I decided that creating a mosaic from the video tapes would solve 
the time delay problem in subsequent conflicts.  My goal is to provide timely
and accurate imagery intelligence to front line commanders using currently available imagery assets. A spin off from this research will be to add imagery 
to computer simulations making them more realistic.

Backgound:
I am working on projecting video images on to a terrain model.
I have a program that creates a polygonal terrain model from digital terrain
elevation data.  I also have a video tape of the terrain model area.  I have
grabbed the images from the video tape.  I have all the information to map
each pixel to the ground coordinates.  The video was produced by a 
stabilized camera in an Remotely Piloted Vehicle.  Since the field of 
view of the camera system is small, the altitude the aircraft flies is
low, and most images are low obliques, I can assume away the curvature of
the earth.

Hardware & Software:  I am primarily using Silicon Graphics Systems. 

Research Thus Far:
So far I've researched the following subject areas to 
find a solution: Photogrammetry, Computer Graphics, Computer Simulation, and Terrain Modeling.

Development Thus Far: 
I can capture the images from video tape and convert them to almost any
format.  I have attempted to rectify the images (convert them to an overhead
view) using the texture mapping and transformations.  However, this assumes the earth is a flat surface and I have run into a bunch of other assorted problems (e.g. Correcting for the change in scale as I progress radially from the 
center of the image to the outside edges).  I now believe Ray Tracing is 
the way to go.

*The real world terrain is not flat it is a polygonal representation of the
Earth's surface.

I am a masters student at the Air Force Institute of Technology.
My thesis work requires me to create an imagery enhanced terrain model.

THANKS FOR ANY ASSISTANCE YOU CAN RENDER.

Art Earl, Captain U.S. Army, AFIT Graduate Student, Department of Engineering Sciences, aearl@afit.af.mil