Hello Dale The reason for the failure is that the UTM projection is not recommended on continental-scaled maps; although the forward projection is well-defined (lon, lat) -> (X, Y), the mathematics for the reverse projection back to (lon, lat) rapidly loses accuracy when you are well away from the central meridian, and in extreme cases the reverse-projection will return a dummy value instead of valid latitude or longitude. For instance, the following reference states:
http://www.georeference.org/doc/universal_transverse_mercator_utm_.htm The accuracy of any Transverse Mercator projection quickly decreases from the central meridian. Therefore, it is strongly recommended to restrict the longitudinal extent of the projected region when using Universal Transverse Mercator projections to +/- 6 degrees from the central meridian This is why the IGRF calculation failed; not simply because the longitude value was not in the value -180 to 180 degree range, but because it was a dummy value! The GX itself was never expecting that the reverse projection itself would fail, and simply fed the dummy value into the "get the IGRF at this location" function. A more severe windowing of your existing grid would likely succeed, especially removing the more northerly section, but I would instead recommend using a conformal map projection if you wish to run this GX on continental-sized data sets. Cheers, Stephen From: [email protected] [mailto:[email protected]] On Behalf Of Dale Bird Sent: May-11-13 8:44 PM To: Geosoft Oasis montaj and Target Subject: [geonet] variable RTP I am trying to use "varyrtp.gx" on the entire North American magnetics data Using parameters: Window size = 750000 Window overlap = 40000 Minimum inclination = 20 Weiner filter option = No Survey height = 300 I keep getting the error "Invalid Longitude" There is no log file Does anyone know how to fix this? d _________________________________________ So many windmills, So few Quixotes - John Lujan _________________________________________ Dale Bird, Ph.D. Bird Geophysical 16903 Clan Macintosh Houston, Texas 77084-1942 + 1-281-463-3816 Office + 1-281-463-7899 Fax + 1-713-203-1927 Mobile [email protected]<mailto:[email protected]> www.birdgeo.com<http://www.birdgeo.com> --- Forum archives can be accessed here: http://lyris.geosoft.com/read/?fourm=geonet You are currently subscribed to geonet as: [email protected]<mailto:[email protected]>. To subscribe or unsubscribe from any of our forums, select the User Forum selection on the Geosoft Community page: http://www.geosoft.com/support/community --- Forum archives can be accessed here: http://lyris.geosoft.com/read/?fourm=geonet You are currently subscribed to geonet as: [email protected]. To subscribe or unsubscribe from any of our forums, select the User Forum selection on the Geosoft Community page: http://www.geosoft.com/support/community
