[Mapserver-users] GeoTIFF Summary

[Rolf Becker]

Hi,

I am new to this list and relatively new to mapserver. Please excuse me for flooding you with 
questions but I would like to summarize and check what I know about GeoTIFF in Mapserver. I have 
already checked the FAQ and the mailing list archieve but I am still a bit confused.

I have a nice GeoTIFF image with 3 bands. Its name is "tct.tif" (with coord. file "tct.tfw"). I 
would like to display it with mapserver but several problems arise.

Could you please comment on the following statements (S) and question (Q) to help clearify my mind:


According to Frank Warmerdam,
http://mapserver.gis.umn.edu/data2/wilma/mapserver-users/0310/msg00512.html ,


it is true that ...


S1) ... all raster data are mapped (classified) to 0..255 before drawing (drawGDAL()).


Q1) How are the 3 bands with 256 values each mapped to one dimension, i.e. 0-255, by mapserver?


S2) ... values above 255 are clipped to 255.


S3) ... one solution is to preprocess data before feeding into mapserver.


S4) ... a second solution is to use the PROCESSING directive in the map-file.


Q2) Are these the only solutions?


Q3) Is it possible to set exact one class (e.g. [pixel]=255) to transparent (unvisible)?


Q4) Without an explicit classification in the map-file (CLASS ... END) the TIFF looks nice in its 
default colors, which looks like an implicit classification to me. If I introduce one explicit class 
which does not cover the whole value range (co-domain) of the pixel values, e.g. [pixel]<10, I will 
have to explicitly classify the rest of the values (>=10), otherwise pixels with unclassified values 
won't be drawn. Is this correct? Is it possible to classify only part of the values and to use the 
default (implicit) classification for the rest?


Q5) My GeoTIFF (tct.tif, tct.tfw, with 3 bands) is drawn with this piece of map-file code:

LAYER
   NAME "tct"
   TYPE RASTER
   STATUS ON
   TILEINDEX "tct_index.shp"
   TILEITEM "Location"
END

in perfect colors!!! Very nice.

The same file will not appear if I use the following code:

LAYER
   NAME "tct"
   TYPE RASTER
   STATUS ON
   DATA "/home/data/map/sulm_data/iwk_data/tctstdverwsul.tif"
END

Why?


Q6) If I use the map-file fragment

LAYER
   NAME "tct"
   TYPE RASTER
   STATUS ON
   PROCESSING "BANDS=2"
   DATA "/home/data/map/sulm_data/iwk_data/tctstdverwsul.tif"
END

I will get a gray scale image which is deemed to be band 2 of the GeoTIFF (who knows :).

But what is the directive PROCESSING "BANDS=1,2,3" for? Isn't it worthless? It simply crashes the 
application with the following warning:
Warning: [MapServer Error]: drawGDAL(): Attempt to classify 24bit image, this is unsupported.


Q7) What is planned in future concerning the current classification scheme?


Q8) Will floating point values for rasters be supported?


Q9) Somewhere in the mail archieve I stumbled across a trick how to query data from raster data but 
I can't find it anymore. Could you please give me a hint or the url?


Q10) What about an update of the FAQ?



Thank you very much for your patience.
This posting is long and maybe annoying but I would be nice if you helped me clearing my confusion.

Regards,
Rolf