Re: [thredds] NetCDF Subset service

• To: <cwardgar@xxxxxxxx>
• Subject: Re: [thredds] NetCDF Subset service
• From: <Terry.Rankine@xxxxxxxx>
• Date: Fri, 25 Jul 2014 03:54:14 +0000

Hi Christian

 

I think Thredds has destroyed my PROJCS data which doesn’t allow my code to 
rewarp it into a different projection.

 

busselton-final-meta.nc-thredds-ncss.nc4 -> subset service “request all”

busselton-final-meta.nc -> original file from HTTP service.

 

http://vhirl-dev.csiro.au/thredds/catalog/dem/catalog.html?dataset=testDatasetScan/busselton-final-meta.nc

 

 

 

ran110@vhirl-dev:~/testing$ gdalwarp busselton-final-meta.nc-thredds-ncss.nc4 
-t_srs "+proj=latlong +datum=WGS84" -co "COMPRESS=DEFLATE" -r cubic 
output.wgs84.cubic.nc  -wo OPTIMIZE_SIZE=TRUE -of netCDF -dstnodata -9999

Creating output file that is 1152P x 2597L.

Warning 5: NOTICE: Format set to NC4C because compression is set to DEFLATE.

Processing input file busselton-final-meta.nc-thredds-ncss.nc4.

Using internal nodata values (e.g. -9999) for image 
busselton-final-meta.nc-thredds-ncss.nc4.

ERROR 1: nBlockYSize = 2631, only 1 supported when reading bottom-up dataset

ERROR 1: busselton-final-meta.nc-thredds-ncss.nc4, band 1: IReadBlock failed at 
X offset 0, Y offset 0

ERROR 1: GetBlockRef failed at X block offset 0, Y block offset 0

 

ran110@vhirl-dev:~/testing$ gdalwarp busselton-final-meta.nc -t_srs 
"+proj=latlong +datum=WGS84" -co "COMPRESS=DEFLATE" -r cubic 
output.wgs84.cubic.nc  -wo OPTIMIZE_SIZE=TRUE -of netCDF -dstnodata -9999

Creating output file that is 1152P x 2597L.

Warning 5: NOTICE: Format set to NC4C because compression is set to DEFLATE.

Processing input file busselton-final-meta.nc.

Using internal nodata values (e.g. -9999) for image busselton-final-meta.nc.

0...10...20...30...40...50...60...70...80...90...100 - done.

ran110@vhirl-dev:~/testing$

 

 

HEADER INFO

 

ran110@vhirl-dev:~/testing$ gdalinfo busselton-final-meta.nc-thredds-ncss.nc4

Driver: netCDF/Network Common Data Format

Files: busselton-final-meta.nc-thredds-ncss.nc4

Size is 946, 2631

Coordinate System is:

PROJCS["unnamed",

    GEOGCS["unknown",

        DATUM["unknown",

            SPHEROID["Spheroid",6378137,298.257223563]],

        PRIMEM["Greenwich",0],

        UNIT["degree",0.0174532925199433]],

    PROJECTION["Transverse_Mercator"],

    PARAMETER["latitude_of_origin",0],

    PARAMETER["central_meridian",117],

    PARAMETER["scale_factor",0.9996],

    PARAMETER["false_easting",500],

    PARAMETER["false_northing",10000],

    UNIT["kilometre",1000,

        AUTHORITY["EPSG","9036"]]]

Origin = (189.659982684810018,6757.539391574399815)

Pixel Size = (0.250000000000000,-0.250000000000000)

 

 

VS

 

ran110@vhirl-dev:~/testing$ gdalinfo  busselton-final-meta.nc

Driver: netCDF/Network Common Data Format

Files: busselton-final-meta.nc

Size is 946, 2631

Coordinate System is:

PROJCS["UTM Zone 50, Southern Hemisphere",

    GEOGCS["WGS 84",

        DATUM["WGS_1984",

            SPHEROID["WGS 84",6378137,298.257223563,

                AUTHORITY["EPSG","7030"]],

            TOWGS84[0,0,0,0,0,0,0],

            AUTHORITY["EPSG","6326"]],

        PRIMEM["Greenwich",0,

            AUTHORITY["EPSG","8901"]],

        UNIT["degree",0.0174532925199433,

            AUTHORITY["EPSG","9108"]],

        AUTHORITY["EPSG","4326"]],

    PROJECTION["Transverse_Mercator"],

    PARAMETER["latitude_of_origin",0],

    PARAMETER["central_meridian",117],

    PARAMETER["scale_factor",0.9996],

   PARAMETER["false_easting",500000],

    PARAMETER["false_northing",10000000],

    UNIT["METERS",1]]

Origin = (189659.982684810005594,6757539.391574399545789)

Pixel Size = (250.000000000000000,-250.000000000000000)

 

 

From: Christian Ward-Garrison [mailto:cwardgar@xxxxxxxx] 
Sent: Friday, 25 July 2014 7:49 AM
To: Rankine, Terry (Mineral Resources, Kensington)
Cc: thredds@xxxxxxxxxxxxxxxx
Subject: Re: [thredds] NetCDF Subset service

 

Hi Terry,

You might expect that when you request all of the data in a dataset, NCSS will 
simply return the original dataset (no subsetting required). That's not how 
NCSS works; instead, it will always create a new dataset, and copy over the 
requested data (which could potentially be everything) from the original.

In this scenario, you might notice that the original and new datasets are 
*structurally* different (i.e. different attributes, scale factors, etc), but 
they are *semantically* equal (i.e. they contain the same data, though it might 
be represented differently).

As far as I can tell, your 2 example files are semantically equal. Are you 
struggling with structural equality issues?

Cheers,

Christian

 

On Mon, Jul 21, 2014 at 12:46 AM, <Terry.Rankine@xxxxxxxx 
<mailto:Terry.Rankine@xxxxxxxx> > wrote:

Hi Guys

 

Is there any other users currently using the netCDF subset service? I am having 
quite a few issues with it and would like to check ‘it’s not just me’

 

This:

http://vhirl-dev.csiro.au/thredds/fileServer/dem/busselton-final.nc

 

is very very different to this:

http://vhirl-dev.csiro.au/thredds/ncss/grid/dem/busselton-final.nc?var=elevation
 
<http://vhirl-dev.csiro.au/thredds/ncss/grid/dem/busselton-final.nc?var=elevation&north=-29.2729&west=113.5915&east=116.2396&south=-35.2422&horizStride=1&accept=netcdf4>
 
&north=-29.2729&west=113.5915&east=116.2396&south=-35.2422&horizStride=1&accept=netcdf4

 

How are others handling THREDDS and CRS changes?

 

Regards

Terry


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