displaying rasters with negative pixel values

[Chris Garrard]

I figured out the problem.  Well, at least how to fix it.  After playing
with it some more, I determined that mapserver wasn't treating the data
set as 8-bit signed, but instead was treating it as 8-bit unsigned.  I
converted it to 16-bit signed, and it worked great. 

Chris 


> -----Original Message-----
> From: UMN MapServer Users List 
> [mailto:MAPSERVER-USERS at LISTS.UMN.EDU] On Behalf Of Chris Garrard
> Sent: Monday, May 08, 2006 10:17 AM
> To: MAPSERVER-USERS at LISTS.UMN.EDU
> Subject: Re: [UMN_MAPSERVER-USERS] displaying rasters with 
> negative pixel values
> 
> Hi Chris,
> 
> Thanks for looking at this.  Here's the map file.  It displays classes
> c5 - c10 just fine, and shows part of the data from the c4 class.  I
> have big blank areas for classes c1 - c3.  If I use either of the
> commented-out processing directives instead of the classes, I 
> still get
> the blank areas.  The image displays fine in other software, so I know
> the data are there.
> 
> MAP
>   NAME utah
>   EXTENT -1510000 -285000 -1020000 375000
>   UNITS METERS
>   IMAGETYPE png
>   SIZE 450 450
> 
>   OUTPUTFORMAT
>     NAME PNG
>     DRIVER "GD/PNG"
>     MIMETYPE "image/png"
>     IMAGEMODE RGBA
>     EXTENSION "png"
>     TRANSPARENT OFF
>   END
> 
>   WEB
>     IMAGEPATH "/webgis/apache/htdocs/tmp/"
>     IMAGEURL "/tmp/"
>   END
> 
>   LAYER
>     NAME mintemp
>     TYPE raster
>     STATUS default
>     DATA '/auto/earth2/ars_data/statedata/utah/ut_tmin.img'
> #    PROCESSING "SCALE=AUTO"
> #    PROCESSING "SCALE=-7,10"
>     CLASS
>       NAME 'c1'
>       TITLE '(-7) - (-6)'
>       EXPRESSION ([pixel] >= -7 AND [pixel] <= -6)
>       COLOR 0 0 255
>     END
>     CLASS
>       NAME 'c2'
>       TITLE '(-5.9) - (-4)'
>       EXPRESSION ([pixel] > -6 AND [pixel] <= -4)
>       COLOR 54 97 255
>     END
>     CLASS
>       NAME 'c3'
>       TITLE '(-3.9) - (-2)'
>       EXPRESSION ([pixel] > -4 AND [pixel] <= -2)
>       COLOR 56 171 255
>     END
>     CLASS
>       NAME 'c4'
>       TITLE '(-1.9) - 0'
>       EXPRESSION ([pixel] > -2 AND [pixel] <= 0)
>       COLOR 0 255 255
>     END
>     CLASS
>       NAME 'c5'
>       TITLE '0 - 1'
>       EXPRESSION ([pixel] > 0 AND [pixel] <= 1)
>       COLOR 145 255 181
>     END
>     CLASS
>       NAME 'c6'
>       TITLE '1.01 - 2'
>       EXPRESSION ([pixel] > 1 AND [pixel] <= 2)
>       COLOR 209 255 105
>     END
>     CLASS
>       NAME 'c7'
>       TITLE '2.01 - 3'
>       EXPRESSION ([pixel] > 2 AND [pixel] <= 3)
>       COLOR 255 255 0
>     END
>     CLASS
>       NAME 'c8'
>       TITLE '3.01 - 4'
>       EXPRESSION ([pixel] > 3 AND [pixel] <= 4)
>       COLOR 255 184 0
>     END
>     CLASS
>       NAME 'c9'
>       TITLE '4.01 - 6'
>       EXPRESSION ([pixel] > 4 AND [pixel] <= 6)
>       COLOR 255 112 0
>     END
>     CLASS
>       NAME 'c10'
>       TITLE '6.01 - 10'
>       EXPRESSION ([pixel] > 6 AND [pixel] <= 10)
>       COLOR 255 0 0
>     END
>   END
> 
> END
> 
> > -----Original Message-----
> > From: Christopher Condit [mailto:condit at sdsc.edu] 
> > Sent: Friday, May 05, 2006 5:59 PM
> > To: Chris Garrard; MAPSERVER-USERS at LISTS.UMN.EDU
> > Subject: RE: [UMN_MAPSERVER-USERS] displaying rasters with 
> > negative pixel values
> > 
> > Hi Chris-
> > Can you send your map file?  I've had great success with 
> > negative raster
> > values when defining my own classes (Sea temperature GeoTIFF 
> > / AAI Grid,
> > for instance).
> > 
> > -Chris
> > 
> > -----Original Message-----
> > From: UMN MapServer Users List 
> > [mailto:MAPSERVER-USERS at LISTS.UMN.EDU] On
> > Behalf Of Chris Garrard
> > Sent: Friday, May 05, 2006 5:16 PM
> > To: MAPSERVER-USERS at LISTS.UMN.EDU
> > Subject: [UMN_MAPSERVER-USERS] displaying rasters with 
> negative pixel
> > values
> > 
> > Hi all,
> > 
> > I have a raster data set that has values from -7 to 10 (mean minimum
> > temps C).  I can't get any of the pixels with values less than -1 to
> > display in mapserver.  I have tried using the processing 
> directive to
> > scale the values and I've tried specifying classes, and 
> neither works.
> > I have also tried different file formats (geotiffs and erdas .img).
> > 
> > Anyone know why this isn't working?
> > 
> > I'm using mapserver 4.8.3 and gdal 1.3.1 on solaris 10.
> > 
> > Thanks for any ideas,
> > Chris
> > 
>