Thank you again. Now I know which direction should I go.This is my goal to have a control over this process using the low-level RasterIO. I browse GDAL github repository a lot and it's very helpful, especially the tests. This time I was confused with WMTS and I needed a support at the begining.
Have a great weekend! Michal pt., 31 maj 2024 o 16:14 Rahkonen Jukka <jukka.rahko...@maanmittauslaitos.fi> napisał(a): > Hi, > > > > You do not need to use GDALTranslate even if may be convenient. In the > RasterIO() function GDALRasterBand C++ API — GDAL documentation > <https://gdal.org/api/gdalrasterband_cpp.html> the region is selected by > using XOff, YOff, XSize and YSize which map directly with -srcwin. But I > was thinking that very soon you’ll ask about how to convert a georeferenced > coordinates into pixel space, and gdal_translate supports that. So maybe > you want to read the source code > https://github.com/OSGeo/gdal/blob/master/apps/gdal_translate_lib.cpp. > And meanwhile you can read and convert data from WMTS with gdal_translate, > enjoy in seeing that it works, and be confident that you will be able to do > the same and more with your own code. If programmers think that way, I do > not know. > > > > -Jukka- > > > > *Lähettäjä:* Michał Kowalczuk <michkowalc...@gmail.com> > *Lähetetty:* perjantai 31. toukokuuta 2024 16.32 > *Vastaanottaja:* Rahkonen Jukka <jukka.rahko...@maanmittauslaitos.fi> > *Kopio:* Even Rouault <even.roua...@spatialys.com>; > gdal-dev@lists.osgeo.org > *Aihe:* Re: [gdal-dev] GDAL WMTS get tiles no documentation > > > > Thank you Rukka, > > Since *-srcwin* and *-projwin* are options only for *gdal_translate* > utility, your suggestion leads me to use *GDALTranslate()* function with > these parameters. > > > > This means that I cannot use directly created WMTS dataset to retrieve > data (using GDALDatasetRasterIO), but create a new (in-memory or > file-based) for each map extent change. > > > > And this is the standard way of doing it? > > Do I understand it correctly? > > > > Michal > > > > pt., 31 maj 2024 o 15:13 Rahkonen Jukka < > jukka.rahko...@maanmittauslaitos.fi> napisał(a): > > Hi, > > > > Before starting to program you can familiar yourself with the topic by > using gdal_translate gdal_translate — GDAL documentation > <https://gdal.org/programs/gdal_translate.html>. > > Play with the -srcwin and -projwin / -projwin_srs options and gather some > trust that is is possible to select and download any part of the large WMTS > layer. Add “-- debug on” and you will see that GDAL downloads tiles > separately just like QGIS. Actually, with WMTS it is the only way to > download data. Maybe you have read the standard already > https://portal.ogc.org/files/?artifact_id=35326. It is not necessary > because GDAL knows what to do, but a review every now and then does not > harm. Especially the TileMatrix and TileMatrixSet things are not > self-evident, but they provide the answer to the question about how a WMTS > client knows which row, col, and zoom to download. > > > > Do not touch the DataWindow. It defines the extent of the whole WMTS layer > and it is used for example if gdal_translate is run without spatial > selection (-srcwin or -projwin). Touch in your future code things which are > equivalent to -srcwin or -projwin of gdal_translate. > > > > -Jukka Rahkonen- > > > > *Lähettäjä:* Michał Kowalczuk <michkowalc...@gmail.com> > *Lähetetty:* perjantai 31. toukokuuta 2024 15.45 > *Vastaanottaja:* Even Rouault <even.roua...@spatialys.com> > *Kopio:* Rahkonen Jukka <jukka.rahko...@maanmittauslaitos.fi>; > gdal-dev@lists.osgeo.org > *Aihe:* Re: [gdal-dev] GDAL WMTS get tiles no documentation > > > > Hi, thank you for your replies! > As I'm still a newbie especially with WMTS. I need to take a step back to > the basics. Let's forget about multithreading for now. > > - I'm in the stage that I can open a dataset using WMTS service path > from data provider > - I can list subdatasets and open the selected layer as a new dataset > using path from *SUBDATASET_id_NAME*. > - This dataset reports large height and width values, which is obvious. > - The first question is how to read any fragment from this dataset > using *GDALDatasetRasterIO*. > Is there a similar way to *SpatialFIlter *from vector layers? > I see in the docs there is a *<DataWindow>* tag for a local service > descriptions which defines extents of the data. Does it mean that for each > map extent change I need to create a new local XML file and open a new > dataset to read demanded bbox? > Is this the only way for doing it? > - From other site I noticed that QGIS downloads tiles separately? But > how it knows which row/col and zoom should be used in GET request? Does > it use GDAL for WMTS reading at all? > > I will be grateful for any tip and trucks for a newbie ;-) > > > > Regards, > > Michal > > > > śr., 29 maj 2024 o 12:41 Even Rouault <even.roua...@spatialys.com> > napisał(a): > > Hi, > > The WMS cache (which is used underneath by the WMTS driver) writes each > tiles in a separate file. So if you use multi-threaded, as long as you read > in parallel different GDALDataset* object on the WMTS filename, and read > disjoint areas, that should be fine. There might be a slight risk of things > going bad if you happened to read the same tile from different GDALDataset* > object at the same time, as it could potentially read a partially written > cached tile, or concurrently write the tile in the cache and corrupt it. > The logic is in frmts/wms/gdalwmscache.cpp > > Even > > Le 29/05/2024 à 10:14, Michał Kowalczuk via gdal-dev a écrit : > > Because this is not clear in documentation, especially in WMTS driver > docs, my question is strictly about this issue to programmers who have > already explored this topic. > > > > Regards > > Michal > > > > W dniu śr., 29.05.2024 o 10:04 Rahkonen Jukka < > jukka.rahko...@maanmittauslaitos.fi> napisał(a): > > 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 <j...@jimenezshaw.com> > *Lähetetty:* keskiviikko 29. toukokuuta 2024 10.41 > *Vastaanottaja:* Rahkonen Jukka <jukka.rahko...@maanmittauslaitos.fi> > *Kopio:* Michał Kowalczuk <michkowalc...@gmail.com>; > gdal-dev@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@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-boun...@lists.osgeo.org> *Puolesta *Michal > Kowalczuk via gdal-dev > *Lähetetty:* keskiviikko 29. toukokuuta 2024 9.08 > *Vastaanottaja:* gdal-dev@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 > > _______________________________________________ > gdal-dev mailing list > gdal-dev@lists.osgeo.org > https://lists.osgeo.org/mailman/listinfo/gdal-dev > > > > _______________________________________________ > > gdal-dev mailing list > > gdal-dev@lists.osgeo.org > > https://lists.osgeo.org/mailman/listinfo/gdal-dev > > -- > > http://www.spatialys.com > > My software is free, but my time generally not. > >
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