ETOPO1 Question

I've trying to map ETOPO1 data but I keep hitting road blocks.

1. I've tried is using the etopo command provided by MATLAB but for ETOPO1 it requires a .flt file which I can't seem to find on the web. Does anyone know where that information can be found?

2. I've loaded in the terrain manually using

terrain = fread(fid, [10801, 21601], 'int16');

The data is indexes longitude by column and latitude by rows. Both are in arc-minute increments (1/60 of a degree) and they begin at -180 and 90 respectively. The data at each cell is the altitude at that given location. But I can't figure out how to create the proper referencing vector for the geoshow function

geoshow(terrain, R, 'DisplayType', 'mesh')

What form should R take?

Answer 1

[Kelly Kearney]

A reference vector is simply a 1 x 3 vector:

[cells/degree north-latitude west-longitude]

So in your case, this would be:

 R = [1/60 90 -180];
 geoshow(terrain, R, ...);

However, I would caution against plotting the whole dataset... it's much higher resolution that your computer monitor could possibly display. For whole world display, you should probably downsample by at least 10.

As for the .flt files, they're available here under the link for whole-world grids (binary):

http://www.ngdc.noaa.gov/mgg/global/global.html

Just rename the files to match Matlab's expectation (remove _f4).

[Kelly Kearney]

Oops, that should be

R = [60 90 -180];

Answer 2

[Walter Roberson]

Here is an indication of the format of .flt files:

http://www.mathworks.com/matlabcentral/newsreader/view_thread/237232