[mapserver-users] Re: displaying ERDAS .img files with mapserver

[Puneet Kishor]

On Nov 9, 2011, at 5:43 PM, Puneet Kishor wrote:

> I am looking for some recent tutes on rendering ERDAS .img files. A bit of the background:
> 
> I inherited these data as an ArcMap .mdb dataset which has metadata.xml, a few other sundry files, and inside a directory with .idb extension, many more folders, each containing a .img file, and a corresponding .rrd and .xml file. A simple layer definition like so allows me to get the tiles displaying in the browser (via OpenLayers) --
> 
> 	LAYER
> 		NAME    "lyr"
> 		TYPE    RASTER
> 		DATA    "foo.img"
> 		PROCESSING "SCALE=AUTO"
> 		STATUS  ON
> 		OFFSITE 0 0 0
> 	END
> 
> But, the tiles don't make for a continuous image. I can see the tile boundaries. Besides correcting that, I would also like to be able to apply different color ramps, and, finally, I would like to be able to query either single pixel values (click on the map and get the underlying value), or some kind of stats on pixels in an area.
> 
> Would appreciate any tutorials/write-ups if anyone has done this.
> 

I solved the above by specifying a PROCESSING directive with appropriate min and max values, and now I get a nicely rendered image. However, I get the following in the ms logs --

> [Thu Nov 10 12:45:43 2011].545705 LoadGDALImage(layer): NODATA value -3.40282e+38 in GDAL
> file or PROCESSING directive largely ignored.  Not yet fully supported for
> unclassified scaled data.  The NODATA value is excluded from auto-scaling
> min/max computation, but will not be transparent.

In this particular dataset, the NODATA value is -3.40282e+38. It well might be different in a different dataset. I am assuming MapServer is carping because I could have set NODATA value somewhere, but didn't, because I don't know how to do that. How do I prevent this error message?


Additionally, my rendered image is grayscale. How can I apply a color ramp to this image? For example, instead of from white to black, I would like it to be from white to red or black to yellow (or whatever). Is there a way to do this without having to specify a color value for each of the 256 pixels?


--
Puneet Kishor