[Gdal-dev] Data format

[Clay, Bruce]

I used the code from the tutorial to create a small app to parse data
from a DEM file.  After a few retries I got Microsoft to accept the GDAL
lib and give me results from the data file.  When I use RasterIO I get
back a buffer full of floats.  How do I interpret them?  Is that based
on the data file read or is that a standard for all vector data?

The data file I opened is a DEM file from the GTOPO30 data set.

The origin is 20.0, 40.0 I assume this is latitude and longitude.

The pixel size is 0.008333, -0.008333.  Does this represent the distance
between values in degrees?  What does the negative number represent?

The GetRasterxxx methods say that the file data 4800 x 6000 x 1.  Does
this mean that only the elevation data is in the file?

The bands are reported to be 4800 wide. Based on the file names in the
GTOPO30 data set it looks like they cover 40 Deg. Longitude but
differing coverage in latitude.  

I am trying to find the elevation for specific coordinates based on
latitude and longitude input.

When I was compiling the program I thought I saw a conditional config
file for compression support  but I could not open a gziped file.  Is
this expected?

Sorry if these are dumb questions.


Thanks in advance for your help.

Bruce Clay
bclay at ball.com