Page 216 - MATLAB Recipes for Earth Sciences

Recommended Reading 211

As an example, we use the image stored in the fi le naivasha_georef.jpg
and digitize the outline of Lake Naivasha in the center of the image. We call
the new function minput from the Command Window using the commands

data = minput('naivasha_georef.jpg')

The function first calls the coordinates for the limits of the x- and y-axis for

the reference frame. We enter the corresponding numbers and press return
after each input.

Specify xmin! 36.1
Specify xmax! 36.7
Specify ymin! -1
Specify ymax! -0.3

Next the function reads the fi le naivasha_georef.jpg and displays the image.
We ignore the warning

Warning: Image is too big to fit on screen; displaying at 33%

and wait for the next response
Click on lower left and upper right corner, then <return>

The image window can be scaled according to user preference. Clicking on
the lower left and upper right corner defines the dimension of the image.

These changes are registered by pressing return. The routine then references
the image to the coordinate system and waits for the input of the points we
wish to digitize from the image.
Click on data points to digitize, then <return>

We finish the input again by pressing return. The xy coordinates of our digi-

tized points are now stored in the variable data. We can now use these vec-
tor data for other applications.

Recommended Reading

Abrams M, Hook S (2002) ASTER User Handbook - Version 2. Jet Propulsion Laboratory
and EROS Data Center, USA
Campbell JB (2002) Introduction to Remote Sensing. Taylor & Francis
Francus P (2005) Image Analysis, Sediments and Paleoenvironments - Developments in
Paleoenvironmental Research. Springer, Berlin Heidelberg New York
Gonzales RC, Eddins SL, Woods RE (2003) Digital Image Processing Using MATLAB.
Prentice Hall