[OSM-talk] JOSM Hack Trick for DigitalGlobe Premium Dual Images (Avoid automatic switch to high-res at z18)

Pierre Béland pierzenh at yahoo.fr
Fri Jan 25 21:25:36 UTC 2019

For the #ebola2018 OSM Response, OSM-RDC is using DigitalGlobe Premium imagery for the Tasking Manager project 5660 https://tasks.hotosm.org/project/5660.
DigitalGlobe Premium superposes two images in this area. The first image is clearer and more recent but with lower resolution. Buildings look tiny and it is hard to trace precisely. The second image is relatively obscure and sometimes have clouds.
We can trace first with high res imagery and later switch to the lower resolution to compete the tracing. But
when zooming-in with JOSM, there is an automatic switch from low to high res image at the 40 meters scale (zoom 18). 

How to avoid this behavior  and stick with the low res imagery ? 

This is the Hack! We simply create a second TMS entry in the Imagery panel using the tms[17] prefix. Using this, the image is stretched when we zoom-in up to 40 meters. Even if we have a pixelated image, it is easier to align and trace along the building outlines.

see https://twitter.com/pierzen/status/1088904024626249728
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