[gdal-dev] [Proj] Pixel Shifts When Warping

[Markus Neteler]

On Sun, May 17, 2015 at 1:32 PM, Even Rouault
<even.rouault at spatialys.com> wrote:
> Le dimanche 17 mai 2015 12:54:44, Markus Neteler a écrit :
>> On Sun, May 17, 2015 at 6:44 AM, Yuta Sato <yutaxsato at gmail.com> wrote:
>> > Dear GDAL and Proj Developers and Users:
>> >
>> > I am really frustrated when the MODIS HDF file converted into GeoTiff
>> > with GCS projection never match with the same MODIS file  converted from
>> > MODIS Reprojection tool.
>>
>> We had this issue in the past, too, for our "EuroLST" project
>> (gap-filling of all LST maps for Europe, see http://gis.cri.fmach.it/eurolst/).
>> Solved since then, see below.
>> ...
>>
>> > Do you have any idea on which is more precise: gdalwarp or MRT? Or there
>> > is any way in gdalwarp to get the same image as MRT gives?

An addition:

For our EuroLST project we use EU LAEA as target projection. In our
tests (we made a lot) the MRT results came out shifted by 0.5 -1.0
pixel since MRT does not support a datum or ellipsoid for LAEA (LA in
MRT), instead it supports only a sphere when reprojecting from MODIS
sinusoidal.

Using recent GDAL, gdalwarp does the reprojection from MODIS
sinusoidal to EU LAEA correctly.

>> You may take a look at
>> http://pymodis.fem-environment.eu/
>>
>> pyModis >= 1.0 comes with fast GDAL support (way faster than MRT).
>>
>> The details of the gdalwarp usage you find in the source code here:
>> https://github.com/lucadelu/pyModis/blob/master/pymodis/convertmodis_gdal.py
>
> Markus,
>
> for the sake of my curiosity, could you explain what specific stuff it does
> compared to gdalwarp ? I quickly skimmed through the file and only saw regular
> use of the GDAL warping API. But perhaps I missed something.

pyMODIS is a set of scripts and a library to perform the download of
large numbers of MODIS HDF/XML files (think cronjob), it creates a
mosaic of several tiles, it extracts specific information from
bit-encoded MODIS quality assessment layers of different product types
etc.

Essentially a ready to use product which happily uses GDAL as a backend.

Markus

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