Hughes, B. wrote:

> Yes, that's the one. "000" for longitudes 000 to 090, "090" for 090 to
> 180, "180" for 180 to 270, lastly "270" for 270 to 360. Apparently only
> files needed are the megt*.img ones too.
> 
> What confused me at first was how the megt00n000hb.img to megt00n270hb.img
> tiles are really for the southern hemisphere too. As you might have
> already discovered, it goes southward from 00*n* to 44s and for northward
> is 44n to 88n. Oh, and watch out for those missing 2 degrees at the poles.
> I finally worked that out for a orthographic rendering which pieces all
> the tiles together for a spherical image map I used afterward. Polar tiles
> were shifted up or down by about 6% of a unit, for my unit-sized tiles
> which are 30 X 30 degrees each.
> 
> I'm using 3DEM, http://www.visualizationsoftware.com/3dem/downloads.html ,
> to convert those IMG files to bitmaps and it's both free and very good at
> manipulating or displaying them.
> 
There is no problem with the interpretion of the tiles and their formats. 
I have been using a self-written program to convert the 4x4 tile map 
row-by-row into two full-sized and scaled-down grayscale PNGs. 
See: http://www.cip.physik.uni-muenchen.de/~wwieser/render/img/mars/

It's just that I got a bit confused about the coordinate system on 

(NASA) so I was not sure if everybody was using the same zero 
meridian. But from searching the net and comparing the names of the 
locations (Isidis Planitia, etc) to pixel locations on the spherical 
projections, I now think I can correctly locate the landing sites on 
the map. 

> P.S.
> Something strange about the Mars image/bump maps I got from
> www.space-graphics.com was that I needed to rotate a little to align with
> POV's map_type 1, 'rotate (+80.88-175.2)*y', or else it was offset from
> the wrapped ends. Using the start/end wrapping point to judge where the
> planet surface features are when the camera is directly along -z (or +x if
> not rotating away from the 0 degree longitudinal line) it makes it a
> little tricky if that line isn't at zero.
> 
I did not come across that problem. I measured several outstanding points 
(in maris vallineris, a volcano) and the topo map matches the color map. 

The yellow-blue image map I was using before needed such hand-tweaking 
but not the current one. 

Wolfgang

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