Hello Michael, et al.,
I have just joined moments ago,
background in GIS, GPS mapping, helicopter
pilot. I note your comments about misaligned GPS data.
Just wondering about the map projections
and datum in use in the disaster area. Most
recreational GPS receivers are set to WGS 84
which may not line up very well with what is
probably a very localized datum for Nepal. I
understand from media reports that the earthquake
actually caused terrain shifts of up to 3 m which
might account for some of the discrepancies seen.
I may not be on the right track here but
will help further if possible.
Thanks, Cheers . . . . . . . . Springfield Harrison, Canada
At 03-05-2015 23:56 Sunday, Michael Krämer wrote:
Hi,
for me the "gold standard" for image alignment
in OSM are gpx traces with high quality. If no
traces are available - which likely applies to
most of Nepal - Bing is the standard to use. In
either case adjust any other imagery to match the alignment of the standard.
But now the limitation: Some of the imagery
currently in use with HOT shows some difference
compared to Bing. But this is not a simple
shift. To my limited understanding this comes
from the correction applied to the image.
Especially in mountains this is difficult -
which likely is especially true for the
Himalayas. But keep the distances in mind: With
high resolution images a shift of let's say 10 m
is pretty visible - but should not really matter too much in real live.
In any case: Try to align any of your work with
Bing. Leave any misaligned data for now.
Michael (user Ohr)
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