When it comes to a website, generally, a good way of getting background
maps (rasters) is XYZ tiles or similar with the different zoom levels.
Each higher zoom level doubles the amount of tiles needed, so the way to
avoid too many tiles taking up too much space is to reduce the number of
zoom levels needed to some realistic amount. The tiles are generally all
the same size 256x256 pixels and it works very well in a web client over
all different speeds of connection. You start at the lowest level and
then zoom in to the next level and so on. This is how it is possible to
do it over slow small devices such as phones, only downloading the tiles
that actually need to be displayed at that point.
I am not sure if this is what you are referring to or something that
actually loads in the Qgis canvas, in which case the above might not be
relevant. But I have worked with many raster tiles loaded off the hard
disk as backgrounds and generally there has not been a speed issue for
them. However if you don't have enough RAM, this could create a problem.
If you expect to use a lot of swap then buy a large SSD and set this up
as you swap partition, since it will perform much better than a regular
hard disk.
Also look at what resolution the downloaded imagery is, you may not need
more than 1 metre resolution depending on how much you need to zoom in,
so that you could be able to reduce the filesizes quote a lot.
On 10/07/22 20:58, Andreas via Qgis-user wrote:
Hello!
First I have to say that I'm a qgis beginner and I'm not very much into
the concepts about functions and design behind QGIS, and GIS in general.
So please apologize for any strange question...
Currently I have an older core i7 with 8 GB RAM running QGIS Desktop
3.10 on Linux Mint 20.3, which I know is already obsolete but it's in
the repositories of this most recent Linux Mint LTS version, and I need
a stable system that does not break due to a library update etc.
I want to visualize data points, that I collect "on the road" over large
distances, on the fly. So far so good everything works very fine,
opening the data log file in a text layer with surveillance of log
changes. Except having an offline background map for orientation. There
is not always internet connection, and also it would be quite expensive
to continuously download the tiles from a server over LTE.
Up to now I tried using shapefiles from geofabrik.de, but even importing
a small town takes minutes.
Also the plugins for downloading xyz tiles will not work, as I need
whole europe offline available in the best case, at least a whole
country.
Then I imported a .osm file in a spatialite database but there are
thousands of attributes I have to chose from, not knowing which ones,
and also I cannot import more than a small region due to the insane time
it takes.
The last thing I tried was a download of Germany vector tiles from
maptiler.com, about 3,5 GB. When I drag and drop it into QGIS, it loads
for hours without coming to an end, there is no information about what
the software is doing (progress bar) or a button to stop the import, so
I finally killed the QGIS process.
I was also looking for GeoPackage maps, as they seemed to have an index
and mbtiles not (which may be what causes the described problems), but
did not find any resources on the net except from a site that provides
the whole planet earth (which is way too much for me).
Yesterday I tried to setup a QGIS Server to set up a WMTS service on the
same machine, but I failed on finding out how to make map data available
on the server (I have to provide a QGIS project file but as I already
wrote, I was not even able to import a simple all-germany map).
So, finally, there must be something I'm missing or I don't understand.
If you have a smartphone or a Garmin GPS, you can easily download a map
for whole germany that is about 2 GB, that can be imported in a few
seconds, then accessed very performant by slow processors with tiny
available memory. I also don't see why it should be necessary to go via
a WMTS Server (http) to provide map data in a way QGIS can them handle
with performance - how is the server getting its high performance, and
why QGIS can't do it on it's own? Or can it - how??
Any hints about how I can get large area offline maps into QGIS are
highly appreciated - thank you very much in advance!
Andreas
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