[mapserver-users] GRIB files - gdal_translate

Wed May 20 12:41:43 PDT 2009

Hi people,

I used gdal_translate in the GRIB file I want to show with mapserver, 
but there still is something wrong. The following is a partial output 
from it:

Driver: GRIB/GRIdded Binary (.grb)
Files: data\raster\T126L28.grb
Size is *161, 98*
Coordinate System is:
.....
Origin = (-150.000000000000000,-61.246000000000002)
Pixel Size = (0.938000000000000,-0.001836734693878)
Corner Coordinates:
Upper Left  (-150.0000000, -61.2460000) (150d 0'0.00"W, 61d14'45.60"S)
Lower Left  (-150.0000000, -61.4260000) (150d 0'0.00"W, 61d25'33.60"S)
Upper Right (   1.0180000, -61.2460000) (  1d 1'4.80"E, 61d14'45.60"S)
Lower Right (   1.0180000, -61.4260000) (  1d 1'4.80"E, 61d25'33.60"S)
Center      ( -74.4910000, -61.3360000) ( 74d29'27.60"W, 61d20'9.60"S)
Band 1 Block=*161x1* Type=Float64, ColorInterp=Undefined
  Description = 0[-] MSL (Mean sea level)
  Metadata:
    GRIB_UNIT=[Pa]
    GRIB_COMMENT=Pressure reduced to MSL [Pa]
    GRIB_ELEMENT=PRMSL
    GRIB_SHORT_NAME=0-MSL
    GRIB_REF_TIME=  1242453600 sec UTC
    GRIB_VALID_TIME=  1242453600 sec UTC
    GRIB_FORECAST_SECONDS=0 sec
....

As u can see the size according to the its header is 161x98, but all the 
bands are related as 161x1 block. Why does it happen? Another thing I 
noticed is that the dif between upper and lower latitude in the corner 
coordinates is very small (-61.246 to -61.426).

The issue is that, when mapserver renders this layer it only draws a 
straight line below South America, exactly where the whole image should 
start, as my CTL below shows.

dset ^T126L28.grb
title pac/sa/atlan sector: troposphere file
undef 1e+20
dtype grib
index ^T126L28.gmp
xdef 161 linear -150.000015 0.937500
ydef 98 levels
-61.246 -60.311
-59.376 -58.441 -57.506 -56.571 -55.636 -54.701 -53.766 -52.831 -51.896 
-50.961
-50.026 -49.091 -48.156 -47.221 -46.286 -45.350 -44.415 -43.480 -42.545 
-41.610
-40.675 -39.740 -38.805 -37.870 -36.935 -36.000 -35.065 -34.130 -33.195 
-32.260
-31.325 -30.389 -29.454 -28.519 -27.584 -26.649 -25.714 -24.779 -23.844 
-22.909
-21.974 -21.039 -20.104 -19.169 -18.234 -17.299 -16.364 -15.429 -14.493 
-13.558
-12.623 -11.688 -10.753  -9.818  -8.883  -7.948  -7.013  -6.078  -5.143  
-4.208
 -3.273  -2.338  -1.403  -0.468   0.468   1.403   2.338   3.273   
4.208   5.143
  6.078   7.013   7.948   8.883   9.818  10.753  11.688  12.623  13.558  
14.493
 15.429  16.364  17.299  18.234  19.169  20.104  21.039  21.974  22.909  
23.844
 24.779  25.714  26.649  27.584  28.519  29.454
zdef 7 levels
1000 925 850 700 500 300 200   ===> set Z 1 ou 2 ou 3 ... ou 7 (GRADS)
tdef 1 linear 6Z16may2009  6hr
vars 15
psnm      0    2,102,  0,  0 SEA LEVEL PRESSURE [hPa]
tsfc      0  187,  1,  0,  0 SURFACE TEMPERATURE [K]
prec      0   61,  1,  0,  0 TOTAL PRECIPITATION [Kg/m2/day]
cbnv      0   71,  3,  0,  0 CLOUD COVER [0-1]
role      0  114,  8,  0,  0 OUTGOING LONG WAVE AT TOP [W/m2]
mask      7  137,100 MASK [-/+]
uvel      7   33,100 ZONAL WIND (U) [m/s]
vvel      7   34,100 MERIDIONAL WIND (V) [m/s]
omeg      7   39,100 OMEGA [Pa/s]
fcor      7   35,100 STREAM FUNCTION [m2/s]
potv      7   36,100 VELOCITY POTENTIAL [m2/s]
zgeo      7    7,100 GEOPOTENTIAL HEIGHT [gpm]
temp      7   11,100 ABSOLUTE TEMPERATURE [K]
umrl      7   52,100 RELATIVE HUMIDITY [no Dim]
umes      7   51,100 SPECIFIC HUMIDITY [kg/kg]
endvars

Can someone help me to find out what is happening?

Tks a lot

Roberto Garcia

Frank Warmerdam wrote:
> Roberto Garcia,MSc wrote:
>> Hi, tks for the answers.
>>
>> According to my gdainfo output file attached, can anyone tell me what 
>> element could be a CLASSITEM?
>
> Roberto,
>
> In MapServer you always classify rasters based on the item [pixel] but
> you do not need to explicitly state a classitem.
>
> This is a relatively simple example of raster classification.
>
> LAYER
>   NAME grid1
>   TYPE raster
>   STATUS default
>   DATA data/float.tif
>   CLASS
>     NAME "red"
>     EXPRESSION ([pixel] < -3)
>     COLOR 255 0 0
>   END
>   CLASS
>     NAME "green"
>     EXPRESSION ([pixel] >= -3 and [pixel] < 3)
>     COLOR 0 255 0
>   END
>   CLASS
>     NAME "blue"
>     EXPRESSION ([pixel] >= 3)
>     COLOR 0 0 255
>   END
> END
>
>> I can see my grib using Grads but what tool do I use to translate 
>> individual bands into GeoTIFF?
>
> You can use gdal_translate to extract particular bands from a grib file
> as a geotiff (or all the bands).  For instance, the following would
> extract band 3 (total precipitation):
>
> gdal_translate -b 3 T126L28.grb total_precip.tif
>
>> Converting the data on-the-fly to an image is the right way to work? 
>
> Having MapServer access the grib file on the fly rather than depending
> on pre-translated extracts will reduce data duplication and may help
> avoid confusion about what is up to date.  However, it is possible that
> there will be a performance penalty for extracting directly from GRIB.
> If so, it may not be significant enough to matter to you.
>
>> What are the problems with Apache if I do not do so?
>
> I don't see how either approach relates to Apache.  It is a
> data management and possibly performance issue with MapServer.
>
> Best regards,
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