[talk-ph] Remarks about Bing imagery in Cebu city
totor_osm at yahoo.com
Wed Mar 2 12:52:08 GMT 2011
Just a little note about the Bing imagery of Cebu.
In Cebu city and surroundings, the highest available zoom level is old (2004) and has a relatively big offset (10 to 20 meters).
Even worse, the offset seems to depend on the altitude. (Probably because the images were not taken vertically)
On the transcentral highway some sharp curves with steep slopes, even have opposite offsets on the beginning and the end of the curve!
One zoom level lower is recent (2009) and has a small offset that seems stable over big distances.
At the beginning of each tracing session, I aligned each lower zoom level to GPS traces where they were reliable and available. (I use mainly Merkaartor, so the image layer has to be dragged again for each session)
I then traced some roads and aligned the highest zoom level to those new roads, so that the alignment for the highest zoom level was done close to where I was tracing.
Switching between old and new imagery is very confusing. Having to re-align the highest one regularly doesn't help. This is why (in the end) I traced most from the previous to the highest zoom level.
I also noted that some of the available GPS traces are quite inaccurate.
Please check things carefully before to realign roads to exising GPS traces or to the Bing imagery...
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