[Proj] cs2cs the fast way
Gerald I. Evenden
geraldi.evenden at gmail.com
Sat May 30 17:08:00 EST 2009
On Saturday 30 May 2009 5:25:52 pm support.mn at elisanet.fi wrote:
> "Gerald I. Evenden" [geraldi.evenden at gmail.com] kirjoitti:
> > The datum shift may add a few coefficients but we do not have to
> > evaluated a possibly complex datum routine.
> > Obviously, this is not yet ready for prime time.
> Ok. If the results are exactly (to adjustable degree) the same and you can
> do it faster, then you have really improved something.
> BTW: I am sure that there must be several ways to make routines faster for
> example by moving calculations to the initialization phase. Since the
> current computers have huge fast memories that might be a nice resource to
> be used to gain speed (using tables to speed up for example).
> Yes, there is always need for speed. That makes everything run smoother.
> Janne. / MNS Support
There is nothing new with this Chebychev stuff. Back in the '80s proj
generated these Chebychev files for use in the program system called MAPGEN.
Because MAPGEN only made large scale maps (down to 1:250,000) in the mid
latitudes this system worked fine. Also, because we were working on mini
computers where 1Mb was a big thing, the graphic programs did not have to
have all the projection software aboard---only the routine to evaluate the
the two polynomials. Speed and size of the software were both
As for more ancient history: circa the mid 60's there was a popular routine
for doing Transverse Mercator. The interesting bit was the use of bivariate
approximating polynomials. The region was divided into about several zones
in the N-S direction with a set of polynomials for each segment. I do recall
if I ever knew where this version came from but I never saw it again. Of
course this routine was hard-wired for Clarke '66.
The whole religious complexion of the modern world is due
to the absence from Jerusalem of a lunatic asylum.
-- Havelock Ellis (1859-1939) British psychologist
More information about the Proj