Sid images

[Luis F. Franco]

Hi to all.

Has anybody heard of the SID imagem format? I've come across some maps in
that format and it's really great. The compression of it is about 25 to 1
and gives images in diferente scales according  to the needs. 

I suppose it works by having a low resolution image (1:16 of the original)
and then saving the diferences for the levels below. As the image is beying
displayed it gets better. When you zoom in the details are increasingly
better... etc.

Something like that could be done with raster maps in grass? One thing I'd
like to see in grass is a dithering that would make the image look nicer on
screen. When you zoom out you lose all the details of roads etc...

Luís Franco
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Instituto das Comunicações de Portugal
email- luis.franco at icp.pt