Python trig precision problem

Robert Kern robert.kern at gmail.com
Fri May 19 06:21:42 CEST 2006


Cary West wrote:
> Hello all, having a small problem with a trig routine using python math 
> module. This code is designed to convert geodetic coordinates to lambert 
> conformal conic coordinates. It implements the formulas found at 
> http://mathworld.wolfram.com/LambertConformalConicProjection.html .  The 
> problem is that, at least on my machine, the precision is off to the tune of 
> around 1 km, which is unacceptable. (using the calculator found at 
> http://www.deh.gov.au/erin/tools/geo2lam-gda.html ) Anyone have any ideas? 
> here is the offending code.

If you want to do map projections, I highly recommend using PyProj instead of
implementing the calculations yourself. Geodesy is nontrivial, and MathWorld
doesn't tell you half the details you need to take care of.

  http://www.cdc.noaa.gov/people/jeffrey.s.whitaker/python/pyproj.html

-- 
Robert Kern

"I have come to believe that the whole world is an enigma, a harmless enigma
 that is made terrible by our own mad attempt to interpret it as though it had
 an underlying truth."
  -- Umberto Eco




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