[HOT] data alignment to satellite imagery

Springfield Harrison stellargps at gmail.com
Mon May 4 07:07:21 UTC 2015


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)
>_______________________________________________ 
>HOT mailing list HOT at openstreetmap.org 
>https://lists.openstreetmap.org/listinfo/hot




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