[gdal-dev] GDAL WMTS get tiles no documentation

[Rahkonen Jukka]

Hi,

No, I am not sure because I do not program myself. Reading this document https://gdal.org/user/multithreading.html makes me feel that it is possible to do some things in parallel, but the programmer must know how to do it right.

-Jukka Rahkonen-

Lähettäjä: Javier Jimenez Shaw <j1 at jimenezshaw.com>
Lähetetty: keskiviikko 29. toukokuuta 2024 10.41
Vastaanottaja: Rahkonen Jukka <jukka.rahkonen at maanmittauslaitos.fi>
Kopio: Michał Kowalczuk <michkowalczuk at gmail.com>; gdal-dev at lists.osgeo.org
Aihe: Re: [gdal-dev] GDAL WMTS get tiles no documentation



On Wed, 29 May 2024 at 08:59, Rahkonen Jukka via gdal-dev <gdal-dev at lists.osgeo.org<mailto:gdal-dev at lists.osgeo.org>> wrote:
Hi,

When you have a RasterBand  from the WMTS data source, it is abstracted and you can read the raster data just like from any other data source and raster band https://gdal.org/tutorials/raster_api_tut.html#reading-raster-data "There are a few ways to read raster data, but the most common is via the GDALRasterBand::RasterIO() method. This method will automatically take care of data type conversion, up/down sampling and windowing." GDAL knows which tiles to read.

I do not know if the WMTS driver can do parallel tile downloads. If not, it is possible to run many RasterIO() at the same time, each reading data from a different window like in this rasterio document https://rasterio.readthedocs.io/en/latest/topics/concurrency.html.

Jukka, are you sure you can run several RasterIO in parallel (on the same dataset)? in GDAL GeoTIFF you cannot: the cache may be corrupted. In that case I open several datasets over the same file. I do not know about WMTS.


-Jukka Rahkonen-

Lähettäjä: gdal-dev <gdal-dev-bounces at lists.osgeo.org<mailto:gdal-dev-bounces at lists.osgeo.org>> Puolesta Michal Kowalczuk via gdal-dev
Lähetetty: keskiviikko 29. toukokuuta 2024 9.08
Vastaanottaja: gdal-dev at lists.osgeo.org<mailto:gdal-dev at lists.osgeo.org>
Aihe: [gdal-dev] GDAL WMTS get tiles no documentation

Hi GDAL fellows
This is my first post on this mailing list, so I'm asking for understanding.

As all we know the purpose of using WMTS over WMS, I'd like to implement parallel downloading tiles from service using C API.
In my opinion GDAL documentation (https://gdal.org/drivers/raster/wmts.html) says nothing on this topic.
I can get capabilities from WMTS, I can open the selected subdataset but how to get tiles for given extent? I could not find any information how to do it, even in the GDAL tests on github.

I am kindly asking for tips. It also can be in python. How using pure GDAL API fetch tiles to dynamically complete the displayed map. This is my goal.

Thank you!
Michal
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