Geo-referencing raster files

[Jrm]

Hi

I'm a big fan of AlpineQuest pro, it makes everything so much simpler than desktop based GIS software. One thing I like is the ability to geo-reference raster files, however it's not always easy to do on a phone, I ave been resorting to emulators to geo-reference a bunch of PNG maps and saved them in PGD format but it's not ideal. There is obvisouly no Windows version for AlpineQuest, but I was wondering if you'd have recommendations as to what I can use to geo-reference my .png maps on my computer and save them in a format readable by AlpineQuest? I've been trying ArcMAP but not much luck.

[Jrm]

OK I figured out something that works, I'm not sure it's the most optimal solution but it works if anyone is looking at doing this in the future.

- Install QGIS (free, open source)
- In QGIS, install the plugin "Freehand raster georeferencer"
- Use the plugin to open your raster and adjust it to match your basemap.
- Export the worldfile from the plugin toolbar.
- Load the exported woldfile back into QGIS and add as a layer.
- On the new layer, right click, choose "Export", "Save as".

At this point, I tried various formats. I wanted to use GeoPKG as it can be read natively by AlpineQuest without importing. However, in AlpineQuest, my exported GeoPkgs always appeared blank. I had to resort to GeoTIFF, which works, but generate huge files.

- In the export dialog, click "Rendered image". Under "Calculate from", "Layer", choose the layer you're trying to export. Choose a file name and click OK to export.
- The exported .tifs were huge, so I used GDAL to compress them using the following command line:

Code: Select all

gdal_translate -b 1 -b 2 -b 3 -co COMPRESS=PNG -co PHOTOMETRIC=YCBCR -co TILED=YES 'Alice-Oodnadatta.tif' 'Alice-Oodnadatta-Deflated.tif'

- Transferred the output file to AlpineQuest.
- Imported the file to have it convereted to .tif.pgd

The final file is slightly bigger than my original raster and did not seem to lose quality, but as I said this might not be the best way to do this, plus there might be more possible options to use with GDAL

[Psyberia-Support]

Hi Jrm and sorry for the delay,

If you have multiple sheets to georeference then you're right that it's easier with a computer. If your images are correctly named, you even have softwares to automatically calibrate them all at once.
Apart from QGIS, I know that SAS.Planet can also do this, and export the maps in MBTiles or OZF.
There is no reason for the application not to read your GeoPKG maps, this format should be preferred over GeoTIFF for multiple reasons (the import is much faster and lossless between the GeoPKG file and AQ).
You can email me one example file if you want so I can have a look.

If you have only a few images, you can also use the app's built'in tool: https://www.alpinequest.net/en/help/v2/ ... -calibrate
When you're used to it, it's quite fast to use.

Regards
François

[Jrm]

Just noticed that the gdal_translate command line I posted above was wrong, here is the correct one I used:

Code: Select all

gdal_translate -b 1 -b 2 -b 3 -co COMPRESS=DEFLATE -co TILED=YES 'Alice-Oodnadatta.tif' 'Alice-Oodnadatta-Deflated.tif'

Thank you Francois, I'll do another test exporting GeoPkgs from QGIS, and I'll email you if it still doesn't work.

[Psyberia-Support]

For info, the app currently supports raw, deflate, LZW and packbits GeoTIFF compressions, tiled or striped files, and RGB, palette and black/white color models.

[Psyberia-Support]

Hi again Jrm, sorry for the delay,
So I had a look at the GeoPKG map you send me, and the problem is actually a "bug" in the app, when the name of the map does contain spaces.
The workaround right now if to create a map with names not containing spaces.
This will be corrected in the next update.
Sorry for the troubles!

In addition to this, your map does have 7 levels of details, but only have data for the last level, so you need to zoom until the last zoom level to see the map.