[3DEM] USGS TIFF files

[Bill Tivol]

On May 14, 2004, at 1:01 PM, Birgit Woods wrote:

> I am working on creating 3D rendered images of Antarctic terrain. I
> downloaded 3DEM and was eager to use it, however, 3DEM does not seem to
> recognize the Tiff files provided by the USGS. I am looking at LIDAR 
> data
> from Antarctica. The data are publicly available from the following
> website:http://usarc.usgs.gov/antarctic_atlas/filedwnld4lidar-ns.html
> Specifically, I was working with the Victoria (80mb) tiff elevation
> model. 3DEM gives an error when I try to load it.
> If you could help me out it would be greatly appreciated. 
>
Dear Birgit,
	Check the data type of the images.  I don't know what USGS uses, but 
DigitalMicrograph, for example, uses signed, 4-byte pixels as the 
default, and most programs do not treat it properly.  Fortunately, one 
can change to unsigned 2-byte data type, which some of our programs can 
handle.  In your case, you may have RGB images, for which most programs 
allow only 1-byte depth per color.  In that case, you will have to 
scale the original data--changing the data type in DigitalMicrograph 
truncates the data, which would be very bad for you.  Good luck.
Yours,
Bill Tivol, PhD
EM Scientist and Manager
Cryo-Electron Microscopy Facility
Broad Center, Mail Code 114-96
California Institute of Technology
Pasadena CA 91125
(626) 395-8833
tivol at caltech.edu