OK, so basically I'll just stick to the IGRF model. Thanks for the discussion though, it helped pull a few things together in my own understanding.
BTW, since this seems to be an area that you have expertise in, do you happen to have a formula to calculate an end point (lat, long) given a start point, distance and initial bearing? But here's the catch, not using a flat projection (ie, cartesian coordinates), instead, using the reverse of the great-circle bearing calculation (takes a start and end point and gives initial bearing)? I have the great-circle bearing calculation (I'll post it if you want), but it is just a tad too complex for me to reverse. Cheers, Phil. ----- Original Message ----- From: "Phil Scadden" <[EMAIL PROTECTED]> To: "NZ Borland Developers Group - Delphi List" <[EMAIL PROTECTED]> Sent: Wednesday, April 21, 2004 1:42 PM Subject: Re: Fw: [DUG] Converting some code from C > > Why forget it if it is a compas? I (apparently incorrectly) assumed that a > > compas *would* be sensitive. If you take a standard marine chart and want to > > plot a course based on a bearing then you may or may not be taking magnetic > > declination into account (ie, true north vs magnetic north). In NZ, although > > the variance is only 2-3 degrees accross the country, the declination itself > > ranges from about 21 to 23 degrees. > > You are wondering though whether its worth getting a total field map for > NZ (which is a raster not a conveniently calculated spherical harmonic > because it reflects the crustal geology) instead of just using the numbers > from the IGRF. I am contending that you couldn't detect the difference > between the IGRF model and actual field with a compass. Its not a precise > enough instument. > > ---------------------------------------------------------- > Phil Scadden, Institute of Geological and Nuclear Sciences > 764 Cumberland St, Private Bag 1930, Dunedin, New Zealand > Ph +64 3 4799663, fax +64 3 477 5232 > > _______________________________________________ > Delphi mailing list > [EMAIL PROTECTED] > http://ns3.123.co.nz/mailman/listinfo/delphi > _______________________________________________ Delphi mailing list [EMAIL PROTECTED] http://ns3.123.co.nz/mailman/listinfo/delphi
