Dear Ronaldo,
You can try the following option:
map2=isundef(map1,color(255,255,255))
where map1 is your map with a black background.
I use it long ago, therefore i didn`t tested since there.
I hope will be still useful for you.
regards,
Luis Sandoval
Bolivia
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Centro de Levantamientos Aeroespaciales Y Aplicaciones SIG
para el Desarrollo Sostenible de los Recursos Naturales (CLAS)
Direcci�n: Jordan y Av. Oquendo (Campus Central)
Universidad Mayor de San Simon
Edificio Multiacademico 2do piso
Casilla 5294 telf./fax +591(04)256551
email: [EMAIL PROTECTED]
www.umss.edu.bo/Academia/Centros/Clas/Default.htm
Cochabamba - Bolivia
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