[Qgis-user] large DEM not loading tiles correctly

[Michael.Dodd]

You can see the format via the link (shown in more detail here OS Terrain® 50 | OS Data downloads | OS Data Hub<https://osdatahub.os.uk/downloads/open/Terrain50?_gl=1*19hd950*_ga*MTM1NTcyMjQ5MC4xNjY0MzY3NTYw*_ga_59ZBN7DVBG*MTY2NDM2NzU2MC4xLjAuMTY2NDM2NzU2MS41OS4wLjA.&_ga=2.219085721.1292185665.1664367560-1355722490.1664367560>) they are ascii grid basically numbers so should not have any .jpg issues. It is unfortunate that they chose to make the grid file so difficult to use by chopping it into the many thousands of small squares each within its own folder within other folders within other folder.

From: Qgis-user <qgis-user-bounces at lists.osgeo.org> On Behalf Of Patrick Dunford via Qgis-user
Sent: Wednesday, September 28, 2022 1:14 PM
To: qgis-user at lists.osgeo.org
Subject: Re: [Qgis-user] large DEM not loading tiles correctly


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Hello

This is a raster format? and how large are the tiles?

I spend a lot of time working with raster files often a few thousand at a time. There doesn't seem to be a problem displaying them in Qgis unless they are Progressive Jpeg format, which in more recent years seem to have an issue with one of the third party libraries Qgis uses to import with.
On 29/09/22 00:32, Michael.Dodd via Qgis-user wrote:
I am trying to put together the 50m uk DEM e.g. https://www.data.gov.uk/dataset/835cf20a-8feb-4394-8b30-dcfe840ac13d/os-terrain-50-dtm<https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.data.gov.uk%2Fdataset%2F835cf20a-8feb-4394-8b30-dcfe840ac13d%2Fos-terrain-50-dtm&data=05%7C01%7Cmichael.dodd%40open.ac.uk%7Ce252ba17960e47d4459b08daa14af7f3%7C0e2ed45596af4100bed3a8e5fd981685%7C0%7C0%7C637999640602880359%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=0kauz1XTDogmzS2bswO60uWR2EgvdVNCSOPzTKC3pjo%3D&reserved=0> but it often does not work.  The data are supplied as thousands of small tiles that takes ages to unpack and put into a folder to get into qgis, however when you try to load the tiles some work and others don’t and even the ones that do work and display fine sometimes don’t merge to form large tiles and sometimes will form virtual rasters but not merged files.  Basically it is a mess.  I suspect others have done this successfully so any suggestions?
It is particularly odd that some of the tiles will merge and others won’t and that some won’t display if you ask it to load hundreds at a time but if you just add them in a few at a time then they will load and display (in addition to the hundreds already loaded). This suggests various bugs assuming the original data are not in a whole variety of slightly different formats (should all be .asc)




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