Kerstin, The difference between "spherical" and the newer "cartesian" calculation is that Pro applies a "scaling factor" to the "cartesian" value to get closer to the real "spherical" value. Some versions ago the spherical method was _the_ method, but cartesian was added for just this case.
What you need to understand, is that a calculated (cartesian) area value for a polygon in a specific projection is only valid for that projection. If you reproject the data to another projection, the very same calculation will render a different (cartesian) value. That is what the "spherical" approach is addressing, trying to generate a common value regardless of projection. However, as I understand it, the "spherical" approach calculates the scaling factor from the polygon mid point (or centroid?), and applies this to the whole polygon. This is off course going to be inaccurate for larger polygons, but for smaller polygons (like cadastres and smaller counties) this should be just fine. ArcView may only have the cartesian version, hence the difference and similarity you experience. Best regards/Med venlig hilsen Lars V. Nielsen GisPro, Denmark http://www.gispro.dk/ ----- Original Message ----- From: <[EMAIL PROTECTED]> To: <[email protected]> Sent: Monday, September 19, 2005 11:49 AM Subject: MI-L Different area calculation in MapInfo and ArcView Hi, I have problems with the different area calculation in MapInfo and ArcView. The data is an import file from ArcView. If I calculate the area of polygons in MapInfo with SphericalArea function it is more than 1 % smaller than the one in ArcView. The function CartesianArea in MapInfo returns a more similar area calculation to the one in ArcView ? Does anybody has experience ? The projection is Gauss-Krueger. Thank's for help in advance. Kerstin --------------------------------------------------------------------- List hosting provided by Directions Magazine | www.directionsmag.com | To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] Message number: 17921
