What Tyler suggests, is likely the problem. I have the same issues
here in Mexico. The US, IK, etc., are al very well mapped, which is
to say, so many third party resources utilize the maps in these
regions, that over time Google has corrected their raster/vector
sources. About 2 months ago, Google implemented street level maps for
Mexico and most of central/south america. First they start with
maps.google.com, and then mobile maps, and lastly they populate Google
Earth. At this point, they have not yet included Mexico into Google
Earth. During this time, the Mexico street level maps have been
changed 4 times(that I know of), which is to say I noticed the maps
were offline for a period of time(hours, sometimes days), and also
noticed position changes across the entire territory, as well as
segmented changes. These changes have resulted in sometimes the
street-level maps being 4 meters to the east of where satellite images
show the roads, and then 3 meters to the south/west, and so on. Over
time they continue making improvements, and depending on the community
activity of the region, so depends the timeliness and accuracy of the
improvements.
I have had to create intentionally inaccurate maps in order to adjust
for Google's road positions, so the resulting vector overlay's would
be in-line with Google's Satellite street locations.
Eric
On Jan 15, 2008, at 7:31 AM, Tyler Erickson wrote:
In my neck of the woods, the current imagery displayed by Google
Maps and Google Earth imagery are shifted about 10-20m to the east.
You can see this when you compare the Google Maps streets data to
the satellite view (see the following URL). I have noticed the same
thing when uploading GPS data that I collected on the local trails
that are visible in the imagery.
So its possible that is nothing wrong with your WMS layers, but it
is that the Google Maps imagery in your area is not precisely
registered...
Example:
http://maps.google.com/maps?f=q&hl=en&q=ann+arbor,+mi&ie=UTF8&t=h&om=1&ll=42.307451,-83.739821&spn=0.005094,0.009656&z=17
- Tyler
Cranio wrote:
Yes I do use that projection. I don't know if my WMS layers (that I
superimpose on Google) are wrong,
altough they shouldn't (they come from governative sources).
Anyway, the WMS are *not* in S-Mercator, but I think they're
reprojected
correctly.
Christopher Schmidt-4 wrote:
On Tue, Jan 15, 2008 at 01:42:29AM -0800, Cranio wrote:
Hi.
another question. My google layer, when greatly zoomed, appears
to be
lightly shifted in
respect to the WMS ones, a shift of about 10-20m in Latitude and
5-10m in
Longitude.
Is there a way to put an offset somewhere to achieve a perfect
alignment?
No.
Are you using Spherical Mercator? There shouldn't be any shift...
Regards,
--
Christopher Schmidt
MetaCarta
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--
Tyler A. Erickson, Ph.D.
Research Scientist
Michigan Tech Research Institute
3600 Green Court, Suite 100
Ann Arbor, MI 48105
[EMAIL PROTECTED]
www.mtri.org
www.michiganview.org
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