Denali Flythrough

       Orion Sky Lawlor, olawlor@acm.org, 10/26/2001

------------- Elevation and Image Data (final_*) --------------
This is a Landsat MSS satellite image and elevation model
of Mt. McKinley, also known as Denali. The mountain is some 
20,320 feet high-- the largest peak in North America-- and
is one of the few locations in the world which look interesting
*without* exaggerating the vertical relief.  These images stretch
160 km on a side, with 40m pixel spacing at the full resolution
4096x4096 image.  Since this is too large to distribute uncompressed
and/or view all at once, only downsampled versions (final_x) are 
presented here.  To save space, the 2x downsampled elevation image
is omitted-- the elevation data has quite poor resolution anyway.

The Landsat image was aquired from the USGS poster "Denali National 
Park and Preserve" and scanned at 150 dpi.  Since the poster is
some four feet wide, the scanning was performed in 34 sections and 
reassembled in software.  Details of the reassemembly process are
in the file "notes_stitch.txt".  One remaining artifact is a 10km
grid-- black lines running through the images.

The elevation data comes from four quads of the USGS 60,000-scale 
base maps, which were converted to digital format by the Eros
Data Center (USGS EDC).  These were assembled and projected into
the UTM zone 5 map projection using the LAS-derived tools from:
	http://www.images.alaska.edu/

The elevation and satellite images, although placed into the same
map projection, still differed slightly in scale, rotation, and 
location.  The final registration was performed by hand-matching
three points in both images and constructing an affine 2D transformation
between the images.  The elevation model was considered more accurate,
and hence the satellite image was mapped to the elevation model.
Details of this process are in "notes_dem.txt".

The resulting coregistered image was nearly six thousand pixels on a side,
and included several useless boundary regions caused by the curved map
projection.  These were trimmed into a 5,300-pixel square image of all good
data, then further trimmed to the power-of-two 4096-pixel images presented
here. Final.jpg contains the entire full-resolution image in JPEG format;
all the other files contain lower-resolution versions.

The elevation images (.dem) are raw binary files, which store the elevation
at each point as a little-endian binary number of meters above the NAD27
datum.  The landsat images (.ppm) are ordinary raw-format Portable Pixel Map
image files, which consist of a small ASCII header followed by packed rgb byte
data.  Both images are stored in left-to-right, top-down pixel order.

The USGS releases the copyright on its maps to the public, so neither the
elevation nor satellite image are copyrighted.  Both are in the public
domain.  

--------------------- Flythough Software ----------------------
The demview.exe program is a VTK 3.2 (www.kitware.com) Win32 application.
You'll need to download and install the VTK DLL from www.kitware.com
before using demview.  

Demview depends on a parameter file which tells it where to find the source
images. To use demview, edit one of the parameter files (demlil.txt, 
demmed.txt, dembig.txt) to point to the directory you installed the elevation 
and texture images to.  Then drag the parameter file onto demview.
If your computer and graphics card are fast, you should be able to use the
medium or large texture and elevation images.  If your computer is slow,
stick with the smaller versions.  For a very fast machine, try removing
mesh decimation, as shown in demhuge.txt.

The interface is standard for VTK and rather unintuitive.  Click and 
hold the mouse to rotate the world-- the position of the mouse controls
the rotation speed and direction.  Right-click to zoom in and out-- the
vertical position of the mouse controls the zoom rate.  Middle mouse button
(or scroll wheel) to pan.

The source and Visual C++ project for Demview are in the code/ directory.
Demview is general in that you should be able to view any two square
elevation and texture images (of the formats described above) by simply
changing the parameter file.

A future release of Demview should include dynamic, viewpoint-dependent
mesh decimation and automatic, out-of-core texture selection and loading.
These features would largely elimate the current trade-off between 
elevation & texture resolution and the amount of bandwidth & memory used.
More intuitive navigation and compressed input formats would also be nice.