[Qgis-user] large DEM not loading tiles correctly

[Patrick Dunford]

I think you are referring to XYZ tiles which are 256x256 pixels. These 
are designed to be put onto a web server and served through WMTS to a 
client. Is that the kind of application you are using them in?

On 29/09/22 01:22, Michael.Dodd wrote:
>
> 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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