Re: [thredds] Providing data access to GIS users

ArcGIS and Mapserver both make heavy use of GDAL, and the fact that they work 
together is probably more a reflection of the shared code base than that they 
necessarily do something correctly.  While GDAL is a great library,  I have had 
similar problems in how it handles OPeNDAP and netCDF files  (it flips the 
images), in cases where the grids etc were clearly specified in CF conventions 
- they were just being ignored and GDAL was imposing its own interpretations.

The question is not whether ArcGIS works with MapServer, but whether the WCS 
service implemented in THREDDS correctly follows the standard, and  provides 
enough information for a client to interpret what it receives correctly. If the 
answer is yes, then we should be talking to ESRI et al. about implementing 
their client correctly to follow the standard.  The equivalent would be saying 
I should change my CF compliant netCDF files to suit GDAL, rather than have 
GDAL learn the standard. 

My $0.02.

-Roy

On Mar 21, 2011, at 3:21 PM, David Neufeld wrote:

> Hi Ethan, Jay,
> 
> Below are my notes about problems with THREDDS WCS and ArcGIS when I last 
> looked at the issue (about 6 mos ago).  I'm not sure if there have been any 
> recent changes in THREDDS or ArcGIS that may have addressed the problem yet.  
> The link to a PDF at the bottom includes some screen snap shots from ESRI's 
> ArcCatalog and ArcMap.
> 
> -Dave
> 
> 
> 
> 
> 
> 
> 
> 
> -------- Original Message --------
>  ArcMap is not correctly displaying coverages from a THREDDS WCS.  The 
> problem appears to be with differences in the DescribeCoverage response 
> in THREDDS compared to MapServer (ArcMap does display WCS coverages from 
> UMN MapServer).  Specifically the problem appears to be related to the 
> way the origin and offset vector are reported.
> 
> ArcMap appears to expect the origin of the Grid to be described in terms 
> of its upperleft corner with the offset vector described accordingly.
> 
> This is a DescribeCoverage response coming from MapServer (note origin 
> is upperleft corner; offset vector for y is negative):
> 
> <gml:RectifiedGrid dimension="2">
> <gml:limits>
> <gml:GridEnvelope>
> <gml:low>0 0</gml:low>
> <gml:high>21600 10800</gml:high>
> </gml:GridEnvelope>
> </gml:limits>
> <gml:axisName>x</gml:axisName>
> <gml:axisName>y</gml:axisName>
> <gml:origin>
> <gml:pos>-180.008333333335 90.008333369335</gml:pos>
> </gml:origin>
> <gml:offsetVector>0.01666666667 0</gml:offsetVector>
> <gml:offsetVector>0 -0.01666666667</gml:offsetVector>
> </gml:RectifiedGrid>
> 
> Currently the DescribeCoverage response from THREDDS contains the 
> following for the gml:RectifiedGrid (note origin is lowerleft corner; 
> offset vector for y is positive).
> 
> <gml:RectifiedGrid srsName="OGC:CRS84" dimension="2">
> <gml:limits>
> <gml:GridEnvelope>
> <gml:low>0 0</gml:low>
> <gml:high>21600 10800</gml:high>
> </gml:GridEnvelope>
> </gml:limits>
> <gml:axisName>x</gml:axisName>
> <gml:axisName>y</gml:axisName>
> <gml:origin>
> <gml:pos>-180.0 -90.0</gml:pos>
> </gml:origin>
> <gml:offsetVector>0.016666666666666666 0.0</gml:offsetVector>
> <gml:offsetVector>0.0 0.016666666666666666</gml:offsetVector>
> </gml:RectifiedGrid>
> </spatialDomain>
> 
> This appears to cause ArcMap to formulate the following GetCoverage 
> request to THREDDS after parsing the DescribeCoverage response (as noted 
> by Kevin Sampson):
> 
> 127.0.0.1 - - [12/Oct/2010:14:53:53 -0600] "GET 
> /thredds/wcs/test/ETOPO1_Ice_g_gmt4.nc?SERVICE=WCS&VERSION=1.0.0&REQUEST=GetCoverage&COVERAGE=z&FORMAT=GeoTIFF&BBOX=-180.008333333333,-89.975,-179.975,-90.0083333333333&WIDTH=2&HEIGHT=2&CRS=&INTERPOLATION=nearest%20neighbor
>  
> HTTP/1.1" 400 331
> 
> At which point THREDDS reports an exception:
> 
> <?xml version="1.0" encoding="UTF-8"?>
> <ServiceExceptionReport xmlns=
> "http://www.opengis.net/ogc";
>  version="1.2.0">
> <ServiceException code="InvalidParameterValue" locator="BBOX">BBOX 
> [-180.008333333333,-89.975,-179.975,-90.0083333333333] minimum point 
> larger than maximum point.</ServiceException>
> </ServiceExceptionReport>
> 
> 
> Full report is available here:
> 
> https://sites.google.com/site/geointeropdemos/home/issues-with-thredds-wcs/WCS_Comments_NGDC_v1.1.pdf
> _______________________________________________
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> http://www.unidata.ucar.edu/mailing_lists/

**********************
"The contents of this message do not reflect any position of the U.S. 
Government or NOAA."
**********************
Roy Mendelssohn
Supervisory Operations Research Analyst
NOAA/NMFS
Environmental Research Division
Southwest Fisheries Science Center
1352 Lighthouse Avenue
Pacific Grove, CA 93950-2097

e-mail: Roy.Mendelssohn@xxxxxxxx (Note new e-mail address)
voice: (831)-648-9029
fax: (831)-648-8440
www: http://www.pfeg.noaa.gov/

"Old age and treachery will overcome youth and skill."
"From those who have been given much, much will be expected" 



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