[Proj] google KML API advice sought

Roger Oberholtzer roger at opq.se
Fri Nov 28 05:18:28 EST 2008

I have been using the google KML API for google map and earth, and all
seems to go well. I would like to do something new with it (for me) and
am soliciting advice.

We have an inertial navigation system (made in-house). I currently plot
the WGS-84 lat/longs that come from our Trimble receivers in google KML.
What I next want to plot is the data after our inertial system as has a
go at it. Our inertial calculations are in northings and eastings, i.e.,

The google KML API does not support plotting northings and eastings. So,
we need to convert back to compatible lat/longs. Our INS does the
calculations in the projection where the data was collected. So, in the
UK, for example, we put it in OSTN02 with a grid shift. So, to convert
back to lat/longs, we would have to do the inverse of this. And each
place we do the calculation would need a similar inverse step.

I am thinking that this is perhaps a more complicated approach than it
need be. Should it not be possible for me to choose a single projection
that is easiest and most accurate for doing the projection and inverse,
and then just do all the INS calcs in that? Note that in this use, I do
not need the northings/eastings. Only 'corrected' lat/longs in the same
WGS-84 datum as the original from the receiver. I know that there must
be some issues of meter distances being different and the effect that
would have on the INS calcs themselves. But I only need a quality as
good as one can see in google earth/map. The INS corrections are over
relatively short distances. Usually less than a kilometer. It is related
to the amount of time we have questionable GPS data.

Should this be a workable approach? If so, what might be a good choice
for the generic projection to use that would do this best in proj (I am
still using 4.4.9...)? I am guessing that it should be one where there
is no grid shift. I do not have a problem with specifying a zone as I
would guess that this would help decrease odd meter scales at various
points around the earth. I have not attempted inverse calculations at
all. There was a discussion about this and the GNU license. I would be
happiest doing this with a library that is more BSD-ish in license. But
that is a later issue. I need to get the concepts sorted!

I'm open to comments.

Roger Oberholtzer

OPQ Systems / Ramböll RST

Ramböll Sverige AB
Krukmakargatan 21
P.O. Box 17009
SE-104 62 Stockholm, Sweden

Office: Int +46 8-615 60 20
Mobile: Int +46 70-815 1696


"On two occasions I have been asked (by members of Parliament!),
'Pray, Mr. Babbage, if you put into the machine wrong figures,
will the right answers come out?' I am not able rightly to apprehend
the kind of confusion of ideas that could provoke such a question.
  - Charles Babbage 1791-1871)
    English computer pioneer, philosopher

And remember:

It is RSofT and there is always something under construction. 
It is like talking about a large city with all construction finished. 
Not impossible, but very unlikely.

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