> When you say that you can calculate for any year, surely those calculations > are dependent on coefficients that are only valid for the current epoch (or > for past epochs). The coefficients are recalculated every 5 years because > simple extrapolation is too innacurate. Haven't looked at the IGRF files, > but assumed that they also work of coefficients. Is that the case?
The IGRF files contain coefficients for each 5 year epoch. "any" year sorry means any year within that range. > The WMM-2000 model is a Low-Resolution model - you don't happen to have a > high resolution model for NZ do you? Now this is an issue as to what you are trying to achieve. The global magnetic model is supposed to represent the mantle-modified main field, free of crustal effects. You map crustal effects by comparing what you actually measure at an xy point and subtract the global model. This leaves you with magnetic anomaly map which is what geophysicists are extremely interested in because it highlights crustal differences. I coded the IGRF model precisely for this purpose - so I can produce anomaly maps from all the total field measurements I have to hand. Now higher-resolution total-field maps (the actual magnetic field at xy) do exist for NZ but I would be very curious as to why you would want one. The local anomalies differ from IGRF by amounts so small that a good magnetometer is needed to detect them. > Cheers, > Phil. > > ----- Original Message ----- > From: "Phil Scadden" <[EMAIL PROTECTED]> > To: "NZ Borland Developers Group - Delphi List" <[EMAIL PROTECTED]> > Sent: Tuesday, April 20, 2004 9:10 AM > Subject: Re: [DUG] Converting some code from C > > > > > where the m is not used in the loop and should have just been > initialised > > > outside it! There's more, but you get the idea. </rant> It also doesn't > help > > > that I'm translating code that carries out calculations that are well > above > > > my comprehension (calculates the 2000 Epoch World Magnetic Model for a > given > > > Lat, Long, Altitude, and Year using spherical-harmonic Gauss > coefficients - > > > whatever they are). Cheers, Phil. > > > > Well those calculations are also available in Fortran if you prefer. I > > translated those earlier in the year into VBA for ArcGIS, but was using > the > > IGRF files so can calculate for any year, any lat/long. > > > > ---------------------------------------------------------- > > 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 ---------------------------------------------------------- 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
