Hi,
So the underlying data might not be very efficient, for example, no internal
Tiling, or compressions used.
What I would suggest is…
1. Create a VRT of all the data you have.
2. Using GDAL Translate convert the VRT into a GeoTiff, with the following
a. NoData Value of -9999
b. Advanced Parameters
i.
NUM_THREADS = ALL_CPUS
ii. BIGTIFF =
YES
iii. TILED = YES
iv. COMPRESS =
LZW
c. Data Type to Float32
3. You can then also use Pyramids for your Maximum zoom levels, I
recommend external, as they can be deleted if you want to change them.
I hope that goes some wat to helping.
Kind Regards,
Richard.
——
Richard McDonnell MSc GIS, FME Certified Professional
FRM Data Management
——
Oifig na nOibreacha Poiblí
Office of Public Works
Sráid Jonathan Swift, Baile Átha Troim, Co na Mí, C15 NX36
Jonathan Swift Street, Trim, Co Meath, C15 NX36
——
M +353 87 688 5964 T +353 46 942 2409
https://gov.ie/opw
——
To send me files larger than 30MB, please use the link below
https://filetransfer.opw.ie/filedrop/richard.mcdonn...@opw.ie
Email Disclaimer:
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——
MSc GIS, FME Certified Professional
——
Oifig na nOibreacha Poiblí
Office of Public Works
Sráid Jonathan Swift, Baile Átha Troim, Co na Mí, C15 NX36
Jonathan Swift Street, Trim, Co Meath, C15 NX36
——
M +353 87 688 5964 T +353 46 942 2409
https://https://gov.ie/opw<https://www.opw.ie>
——
Email Disclaimer:
https://www.gov.ie/en/organisation-information/439daf-email-disclaimer/<https://www.opw.ie/en/disclaimer/>
From: Qgis-user <qgis-user-boun...@lists.osgeo.org> On Behalf Of Michael.Dodd
via Qgis-user
Sent: 28 September 2022 12:32
To: 'qgis-user@lists.osgeo.org' <qgis-user@lists.osgeo.org>
Subject: [Qgis-user] large DEM not loading tiles correctly
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)
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