[Proj] Large scale mapping & Google
al001 at uni-koeln.de
Thu Sep 11 10:30:54 EDT 2008
Gerald I. Evenden wrote:
>Another minor point with google, I bet they are
>*not* using a elliptical projection software.
Indeed they are not, and this is documented on
support sites for KML and for the GE API's both
for COM and the ActiveX Plugin. They use Plate
Carée with sphere A = 6378137.0.
Clifford J Mugnier wrote:
> It has been observed by Military Geodesists
that "A major battle will occur at every Grid Zone Boundary,"
In a number of publications and in the help for
my AirPhoto programme which was written for those
practicing low-level oblique aerial photography
of archaeological sites visible as crop or soil
discolorations to record them on large scale
(1:1000 - 1:5000) maps for monument protection
purposes, I noted this phenomenon with respect
to the original Gauss-Krueger 3 degree grid used
on German maps (Deutsche Grundkarte 1:5000), and
the corollary that all important aerial
archaeological sites are located at the
intersection of four map sheets whose boundaries are on that grid.
An even worse example is the airport of the city
of Basle (Bâle) in Switzerland which is partly in
France and overlooking Germany with three
incompatible map projections (Swiss Oblique TM,
French Lambert Polyconic and German GK 3 degree),
so converting these on the fly to UTM WGS84 with
the very decent datum transformation parameters
available from each country is the only sensible thing to do.
In the former German Democratic Republic, which
was forced to change from the GK 3 degree Bessel
Ellipsoid grid to the Soviet 6 degree Krassovsky
after WW2, a change is now being made to WGS84
UTM 6 degrees for re-mapping. In Bavaria, a
Soldner-Cassini projection and grid centered on
the main church in Münich is still used in many
cadastral records, so that there are at least
three incompatible systems within Germany today that I have encountered.
I think that the most common application of large
scale and largely unpublished mapping in all
developed countries is cadastral survey for
property boundary records many of which are some
variant of TM. The cost of converting the
enormous bulk of data accumulated over centuries
which this represents is perhaps the main reason
why few countries are converting to something
more modern, although pious wishes in this respect are frequently expressed.
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