[postgis-users] Reference vrt datasets in postgis raster

Sun Jul 20 11:41:50 PDT 2014

Hello David, hi all,

thanks for the hint with SRID6842 for MODIS tiles and sorry for the late
reply!

In the meantime I have made several tests still trying to reference
*vrt-files as out-of-database-references in postgis - with no luck. If I
find something useful I'll post it to the group.

Thanks and greetings! Chris

On Mon, Jul 14, 2014 at 5:02 PM, David Haynes <haynesd2 at gmail.com> wrote:

> Hello,
>
> You might want to try this projection:
> http://spatialreference.org/ref/sr-org/6842/postgis/
> This the most accurate projections, despite the description on the spatial
> reference site. I am doing related work and found this calculator at the
> following url
> http://landweb.nascom.nasa.gov/cgi-bin/developer/tilemap.cgi
> There is no projection accuracy error when using SRID 6842.
>
>
>
> On Fri, Jul 11, 2014 at 9:33 AM, Christian Yrrman <yrrman at gmail.com>
> wrote:
>
>> Hi All,
>>
>>
>> I'm a newbie to this group, so hello everyone and thanks in advance for
>> letting me participate :-)
>>
>> After several tests and searching on the net I'm a little stuck with the
>> following problem:
>>
>> I have downloaded a bunch of MODIS tiles (MOD13A1) from [0] that I want
>> to (only) reference in a postgis raster database. These tiles come in hdf
>> containers with several layers in it
>> .
>> - For a start,  I'm only interested in the EVI layer, so I created EVI
>> vrt files with command [1]
>> - This gives me several EVI*.vrt files referencing EVI with the original
>> sinusoidal projection. According to spatialreference.org, the closest
>> SRS match is sr-org6974 [2].
>> - As this is not in postgis, I've imported this into spatial_ref_sys [3]
>> - Next, I'm using the following command to insert the data into raster
>> table "modistest" with the following command:
>>
>> for i in `find / -name "EVI_origSRS*.vrt"`; do
>>         raster2pgsql -s 96974 -R -F -f rast -a $i modistest;
>> done
>>
>> where:
>> "-s 96974" - use the freshly imported MODIS SRS from [2]
>>   -R  Register the raster as an out-of-db (filesystem) raster.  Provided
>>       raster should have absolute path to the file
>>   -F  Add a column with the filename of the raster.
>>   -f <column> Specify the name of the raster column
>>      -a  Appends raster into current table, must be
>>          exactly the same table schema.
>>
>> I've built the index on rast in a separate step (not using switch -I)
>>
>> This populates table modistest (using | psql...), so it looks fine.
>> However when I want to retrieve data from the raster, e.g. via
>>
>> SELECT ST_AsTiff(rast) from public.modistest where id=1158;
>>
>> I get an error message like this
>> ERROR:  rt_raster_from_gdal_dataset: Unable to get data from transformed
>> raster
>> CONTEXT:  PL/pgSQL function "st_astiff" line 20 at RETURN
>>
>> and in the postgresql log I get
>>
>> ERROR 4:
>> `HDF4_EOS:EOS_GRID:"MOD13A1.A2012065.h35v10.005.2012082112322.hdf":MODIS_Grid_16DAY_500m_VI:500m
>> 16 days EVI' does not exist in the file system,
>> and is not recognised as a supported dataset name.
>>
>>
>> So it looks like the layers were not correctly referenced - however I
>> cannot see a mistake. I'm actually using "find / -name "EVI_origSRS*.vrt"
>> to get the full path for the loop (not "for i in *vrt")
>>
>>
>> Any help/advice is highly appreciated! In a next step, I would even like
>> to transform the sinusoidal tile afterwards with ST_transform to epsg:4326.
>> That would be fantastic, I'd have all tiles in original format in the file
>> system and let postgis do all the rest.. :-)
>>
>>
>>
>> Thanks in advance and greetings!
>>
>>
>>
>> Chris
>>
>>
>>
>>
>>
>> [0] MODIS download website
>> http://e4ftl01.cr.usgs.gov/MOLT/MOD13A1.005/
>>
>> [1] command to create vrt files:
>> #!/bin/bash
>>
>> for i in *hdf; do
>>         echo Processing $i
>>         j=`gdalinfo $i| grep SUBDATASET_2_NAME | cut -d '=' -f 2`
>>         echo Extracted $j
>>         gdal_translate -of VRT "$j" EVI_origSRS_$i.vrt
>>
>> done
>>
>> [2] SRS projeciton for MODIS
>> http://spatialreference.org/ref/sr-org/6974/
>>
>> [3] SQL command to insert MODIS SRS
>>
>> INSERT into spatial_ref_sys (srid, auth_name, auth_srid, proj4text, srtext)
>> values ( 96974, 'sr-org', 6974, '+proj=sinu +lon_0=0 +x_0=0 +y_0=0 +ellps=WGS84 +datum=WGS84 +units=m +no_defs ',
>>
>>
>> 'PROJCS["MODIS Sinusoidal",
>> GEOGCS["WGS 84",DATUM["WGS_1984",SPHEROID["WGS 84",6378137,298.257223563,AUTHORITY["EPSG","7030"]],
>> AUTHORITY["EPSG","6326"]],PRIMEM["Greenwich",0,AUTHORITY["EPSG","8901"]],
>>
>>
>> UNIT["degree",0.01745329251994328,AUTHORITY["EPSG","9122"]],AUTHORITY["EPSG","4326"]],
>> PROJECTION["Sinusoidal"],
>> PARAMETER["false_easting",0.0],
>>
>>
>> PARAMETER["false_northing",0.0],
>> PARAMETER["central_meridian",0.0],
>> PARAMETER["semi_major",6371007.181],
>> PARAMETER["semi_minor",6371007.181],
>> UNIT["m",1.0],AUTHORITY["SR-ORG","6974"]]');
>>
>>
>>
>>
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