floating point grass rasters and mapserver - a resume
Neil Best
nbest at LANWORTH.COM
Wed Jul 25 10:09:42 EDT 2007
Can anyone comment on whether this information is still current? Are there
any plans to accommodate GRASS rasters in Mapserver? Thanks for any info or
tips.
Neil
On Sun, 16 Oct 2005 12:43:44 +0200, Jachym Cepicky
<jachym.cepicky at CENTRUM.CZ> wrote:
>very well!
>
>I did it by hand till now (well I do not have so many raster in GRASS
>and ... how often do one need to change the color table?)
>
>could you post this script on GRASS-Addons site?
>(http://grass.gdf-hannover.de/twiki/bin/view/GRASS/GrassAddOns)
>
>Jáchym
>
>On Sun, Oct 16, 2005 at 12:35:14PM +0200, Andrea Antonello wrote:
>> Some time ago I was dealing with mapserver getting maps from a GRASS
location.
>> The maps are all floating point maps and as you (whoever interested) probably
>> followed in a few mails, the result of most of my maps simply resulted in a
>> single color layer (in my case it was yellow).
>> Frank Warmerdam helped me to solve what was solvable and workaround what was
>> "workaroundable".
>> The following is an extract and resume of the mails exchange.
>> Any reply and correction is appreciated.
>>
>> Alright, the problem was not only one, but a bunch concurring:
>> 1) GRASS novalues are not supported and give problems
>>
>> Running gdalinfo -mm on the map, we find that part of the problem is that
>> nodata values are being treated as "nan" (not a number). GDAL and mapserver
>> do not know how to excluse "nan" nodata values from the min/max calculation
>> so the autoscaling gets all screwed up.
>>
>> Here we can see it in the gdalinfo output:
>> <SNIPPET>
>> Band 1 Block=385x1 Type=Float64, ColorInterp=Palette
>> Min=0.000 Max=229172.410 Computed Min/Max=nan,nan
>> NoData Value=nan
>> <SNIPPET>
>>
>> Therefore the min and max have to ge defined and supplied to the map file
with
>> the following:
>> PROCESSING SCALE=min max
>>
>> 2) There is a problem with the creation of color ramps in the case of a big
>> number of not homogeneous distributed values:
>>
>> <SNIPPET>
>> Color Table (RGB with 100001 entries)
>> 0: 0,0,0,0
>> 1: 255,255,0,255
>> 2: 255,255,0,255
>> 3: 255,255,0,255
>> ...
>> <SNIPPET>
>>
>> This is why I had a yellow map. The first 256 values of the color table were
>> used by MapServer for the after-scaling values. Effectively the first 256
>> entries of the color table are all shades of yellow.
>>
>> 3) MapServer does not support the GRASS color rules metadata
>>
>> <SNIPPET>
>> Metadata:
>> COLOR_TABLE_RULES_COUNT=5
>> COLOR_TABLE_RULE_RGB_0=1.000000e+00 4.583448e+04 255 255 0 0 255 0
>> COLOR_TABLE_RULE_RGB_1=4.583448e+04 9.166896e+04 0 255 0 0 255 255
>> COLOR_TABLE_RULE_RGB_2=9.166896e+04 1.375034e+05 0 255 255 0 0 255
>> COLOR_TABLE_RULE_RGB_3=1.375034e+05 1.833379e+05 0 0 255 255 0 255
>> COLOR_TABLE_RULE_RGB_4=1.833379e+05 2.291724e+05 255 0 255 255 0 0
>> <SNIPPET/>
>>
>> The metadata contains the coloring rules that should be applied. However,
>> mapserver does not currently know how to use this sort of color rule
>> metadata. For now the only solution is to recreate classes that are value
>> similar. One problem though is that MapServer classes don't allow applying a
>> range of color to a range of values like GRASS (or QGIS). Applying own
>> CLASSes in the LAYER makes mapserver ignore the color table.
>>
>> The CLASSes option has two main drawbacks:
>>
>> a) The CLASS does not allow color ranges. There is no big solution (only
>> workarounds), if not to wait on the new range based class coloring that Bill
>> Binko has been working on. An implementation of that is available in 4.6.x
>> but it is under revision.
>>
>> b) If we decide to create a set of CLASS rules to get the map drawn "as
if" it
>> was interpolated, you will need to create a lot of rules, which gives big big
>> performance problems in drawing the map. This can however be solved with a
>> PROCESSING command. Here the explanation:
>> The problem is that the class lookup is done once for each "bucket" in the
>> lookup table and that by default there are 65536 buckets. It helps a lot to
>> add the following line in the LAYER definition:
>>
>> PROCESSING "SCALE_BUCKETS=200"
>>
>> This basically alters the resolution of the lookup table but substantially
>> accelerates things.
>>
>>
>>
>> After some testing on what would be the best to do for now, I'm now letting
>> the following bash script snippet for automated creation of the raster part
>> mapfile. It contains the solutions and workarounds reported in this document:
>>
>> # the path to the grass cellheader file
>> absolutepath=$mapsetpath/cellhd/$i
>>
>> echo "LAYER" > rastertmpfile
>> echo " NAME $i" >> rastertmpfile
>> echo " TYPE RASTER" >> rastertmpfile
>> echo " STATUS ON" >> rastertmpfile
>> echo " DATA \"$absolutepath\"" >> rastertmpfile
>>
>> # extract the min and max
>> minmax=`gdalinfo -mm $absolutepath | grep Min | awk -F "=" '{print $2,
>> $3}' | awk '{print $1, $3}'`
>> # extract the gdal computed min and max
>> gdalrange=`gdalinfo -mm $absolutepath | grep "Computed Min" |awk -F
>> "Computed Min/Max=" '{print $2}' | awk -F "," '{print $1}'`
>>
>>
>> # if gdal has problems with colortables and novalues, it is not able to
>> compute the range,
>> # therefore we have to supply it and create a set of ad hoc colorrules
>> if [ "$gdalrange" == "nan" ]
>> then
>> # minmax has the format "123 234", so just extract them
>> min=`echo $minmax | awk '{print $1}' | awk -F "." '{print $1}'`
>> max=`echo $minmax | awk '{print $2}' | awk -F "." '{print $1}'`
>>
>> # define a default colortable, rainbow of grass, but with "bin + 1"
>> number of rules,
>> # to get more colors and give the sensation to be interpolated
>> bins=19
>> delta=$((($max-$min)/$bins))
>>
>> if [ $delta -ne 0 ]
>> then
>> colors[1]="255 255 0"
>>
>> colors[2]="195 255 0"
>> colors[3]="130 255 0"
>> colors[4]="65 255 0"
>>
>> colors[5]="0 255 0"
>>
>> colors[6]="0 255 65"
>> colors[7]="0 255 130"
>> colors[8]="0 255 195"
>>
>> colors[9]="0 255 255"
>>
>> colors[10]="0 195 255"
>> colors[11]="0 130 255"
>> colors[12]="0 65 255"
>>
>> colors[13]="0 0 255"
>>
>> colors[14]="65 0 255"
>> colors[15]="130 0 255"
>> colors[16]="195 0 255"
>>
>> colors[17]="255 0 255"
>> colors[18]="255 0 195"
>> colors[19]="255 0 130"
>> colors[20]="255 0 65"
>>
>>
>> # add the processing commands
>> echo " PROCESSING \"SCALE=$min $max\"" >> rastertmpfile
>> echo " PROCESSING \"SCALE_BUCKETS=100\"" >> rastertmpfile
>>
>>
>> # create the CLASSes, labeling them with the pixel value
>> first=$min
>> second=$(($min+$delta))
>> for j in `seq 1 $bins`
>> do
>> echo " CLASS " >> rastertmpfile
>> echo " NAME \"$first\"" >> rastertmpfile
>> echo " EXPRESSION ([pixel] >= $first and[pixel] <
>> $second)" >> rastertmpfile
>> echo " COLOR ${colors[$j]}" >> rastertmpfile
>> echo " END" >> rastertmpfile
>> first=$(($first+$delta))
>> second=$(($second+$delta))
>> done
>>
>> # add a last CLASSes, due to bash maths limitations
>> echo " CLASS " >> rastertmpfile
>> echo " NAME \"$max\"" >> rastertmpfile
>> echo " EXPRESSION ([pixel] >= $first and[pixel] < $max)" >>
>> rastertmpfile
>> echo " COLOR ${colors[20]}" >> rastertmpfile
>> echo " END" >> rastertmpfile
>> fi
>> fi
>>
>>
>>
>> Hope this helps someone, the script is not very stylistic, but at least it
>> does the job for me. :)
>>
>> Ciao,
>> Andrea
>>
>>
>>
>>
>> --
>> ____________________________________________________________________________
>> HydroloGIS - Environmental Open Source Solutions
>> www.hydrologis.com
>>
>> Andrea Antonello
>> Environmental Engineer
>> mobile: +393288497722
>>
>> "Let it be as much a great honour to take as to give learning,
>> if you want to be called wise."
>> Skuggsja' - The King's mirror - 1240 Reykjavik
>> ____________________________________________________________________________
>
>--
>Jachym Cepicky
>e-mail: jachym.cepicky at centrum.cz
>URL: http://les-ejk.cz
>GPG: http://les-ejk.cz/gnupg_public_key/
>-----------------------------------------
>OFFICE:
>Department of Geoinformation Technologies
>LDF MZLU v Brnì
>Zemìdìlská 3
>613 00 Brno
>e-mail: xcepicky at node.mendelu.cz
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