[Talk-ca] Terminating British Columbia Mosaic imagery

Paul Norman penorman at mac.com
Thu Jun 14 04:58:55 UTC 2018

I will be shutting down the "British Columbia Mosaic" imagery in the 
near or medium future. I set this up in about 2011, and the system has 
been running without many updates since then.

When I started hosting it, we had access to Bing and Yahoo. Between the 
two of them, we had acceptable for the time imagery in Vancouver, and 
poor imagery in Burnaby and east. Living in New West, this was a problem 
for me, so I put together the layer. My main sources were 10cm 2009 
imagery covering Vancouver, 2009 20cm imagery for Burnaby, 2011-2012 
10cm and 40cm for Surrey, and a few other minor sources.

The accuracy and colour range of the Surrey imagery was exceptional for 
the time, and remains exceptional by today's standards. The accuracy of 
other sources was also good, but colours weren't the best. This allowed 
an imagery layer that could be assumed to have accurate positions 
without checking GPS traces everywhere, and its accuracy was ahead of 
the data in OSM at the time, as well as being recent enough.

Times have changed, and we have more imagery hosts. In particular, we 
normally have commercial imagery hosts who will host the open imagery 
that is available, and handle any legal matters about its usage. I 
remember trying to get Bing, Mapbox, or anyone to use the Surrey imagery 
in Surrey, which was better than what they were using in every way and 
free, and having no luck. The data in OSM is frequently more recent than 
the imagery.

Before deciding to shut it down, I reviewed the available imagery in a 
few areas, and recommend defaulting to ESRI imagery in all of the Lower 
Mainland, with the exception of some cloudy parts of Ladner.* In Ladner, 
and if slightly more recent imagery is needed elsewhere, I recommend 
DigitalGlobe Standard Imagery as a lower quality but more recent source. 
Both have excellent alignment. I would not recommend Mapbox Satellite or 
Bing anywhere in the region.

Instead of shutting down, why am I not moving it to a different server? 
Time, mostly. With all of the sources I had used out of date, I'd have 
to find new ones. This would take a lot of time to find and process 
sources, and a lot of time to sort out the legal mess that is open data 
in Canada. I would also probably take a different approach, with 
multiple independent layers that the editor software picks between.

I believe there is still a place for user-hosted imagery, but at least 
here, it will never offer such an increase in quality again, because the 
commercial hosts are offering a much better "baseline".

* Alignment in Hope was possibly worse, but I haven't done extensive 
research into the accuracy of BC Mosaic in that region. I couldn't find 
any good objects to compare with in Whistler, I kept finding stuff had 
changed on the ground, which is a good reason in itself to avoid BC Mosaic.

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