[Proj] Google Earth Accuracy
al001 at uni-koeln.de
Mon Dec 1 14:28:08 EST 2008
MarKus Neteler wrote:
>How about precision in mountainous regions such as the Southern Alps?
>PROJ4/OGR reprojected mountain peak points from geonames.org as
>well as known points from our province are off for > 100m when
>visualized in GE which they match our local orthophotos. Is the positional
>error related to the height of the point (here, satellite orthorectification)?
In GE go to View, Sidebar and turn it on if it's not already
on. There, go to Layers, Primary Database, and uncheck the Terrain
option checkbox. That gives an orthophoto-like view even in the
Alps. You can check this by turning the GE Grid off and on in the
View menu or pressing Ctrl + L.
It's far from perfect, but it's good enough for my application of
mapping archaeological sites visible as crop or soil markings in the
GE images over modest areas. Cliff dwellings are fortunately rare
A more important concern is to increase the apparent resolution of GE
imagery which is normally limited to the number of pixels of the
display screen to approach that of a cadastral map of a small
area. Using the GE lat/lons of image corners which can be found via
KML API routines, one can mosaic multiple zoomed detail images if the
GE raw data is originally from a single good orthophoto or a mosaic
made from several of these or even from a single Digital Globe strip
in some parts of the world like the Nile valley. I have had good
results with this in moderately hilly terrain up to a factor of as
much as 6 in some places on my 1600x1200 display.
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