[OSM-talk] Proposal: Magnetic declination maps overlaid on OSM data

[Ævar Arnfjörð Bjarmason]

The US' National Geophysical Data Center maintains a magnetic
declination model called the International Geomagnetic Reference Field
Model[1] and also provides a program[2] that can give you the
declination for a given set of coordinates on the planet given this
data.

Here's some sample output from that program:

  Model: IGRF2005
  Latitude: 64.14 deg
  Longitude: -21.91 deg
  Altitude: 0.00 km
  Date of Interest:  2008.00

 -------------------------------------------------------------------------------
   Date          D           I           H        X        Y        Z        F
   (yr)      (deg min)   (deg min)     (nT)     (nT)     (nT)     (nT)     (nT)
  2008.00   -16d  32m    75d  34m   13057.2  12517.3  -3716.2  50705.2  52359.4
 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
   Date         dD          dI           dH       dX       dY       dZ       dF
   (yr)      (min/yr)    (min/yr)    (nT/yr)  (nT/yr)  (nT/yr)  (nT/yr)  (nT/yr)
  2008.00      17.7       -0.8         18.4     36.7     59.3     23.3     27.1
 -------------------------------------------------------------------------------

I think it would be awesome to have a declination overlay on OSM
similar to the contour map the cyclemap uses.

If I want to make this happen I guess I'd have to do it myself. I have
no experience producing custom renderings of OSM data or producing
contour-like overlays on the map from a set of coordinates/elevation
data. I guess a very similar technique could be used to get
declination data on the map basically by swapping out elevation for
declination.

If someone here has any pointers on how I'd go about getting started
on such a project that would be most useful.

1. http://www.ngdc.noaa.gov/geomag/declination.shtml
2. http://www.ngdc.noaa.gov/IAGA/vmod/igrf.html