[Qgis-user] large DEM not loading tiles correctly

[Nicolas Cadieux]

Hi,

The asc format is very inefficient and  bad for this.  I would save those as uncompressed tiff.  One way is to make a virtual raster and then save the result as a tiff.  If the data is too big building a pyramid can speed thing up.  Keep in mind windows does have a limite to hoe many layers (files) can be opened at a time. You can save a very big virtual raster as multiple bigger tiles also.  Learning some basic Gdal command line and or python can help you al long way for this type of project, specially if you need to convert thousands of tile.  If you need help with this, contact me. Of course, server and database people will also have their solutions for this problem… it depends on what you what to do with the data.

Nicolas Cadieux
https://gitlab.com/njacadieux

> Le 28 sept. 2022 à 07:33, Michael.Dodd via Qgis-user <qgis-user at lists.osgeo.org> a écrit :
> 
> 
> 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 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)
>  
> _______________________________________________
> Qgis-user mailing list
> Qgis-user at lists.osgeo.org
> List info: https://lists.osgeo.org/mailman/listinfo/qgis-user
> Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.osgeo.org/pipermail/qgis-user/attachments/20221001/b5a50e5c/attachment.htm>