Dear List, I have encountered calculation errors in MapInfo 5.5. I have a dozens of point data sets, which have upwards of hundreds of thousands of points in any one layer. The data is reported from surveys at roughly 1-minute * 1-minute grid intervals. I have a need to sum the points within 1, 2, 4, etc. minute grid squares, as well as count the number of points within these grid cells, there can be hundreds.
I can guarantee that all the points within a cell are counted and summed because the reporting information is recorded at a 1 minute grid intersection in a Lat/Long projection, and my grid cell based aggregation is offset by 1/2 degree to capture all points within the grid square. For a 1-minute grid all the points are in the center of the grid square. My problem comes when using the Sum and Count functions in the SQL Select form window. The results in the New Columns for Count and Sum of the data points attached to the grid polygons are way off. Specifically. The count result is actually the square (i.e. - count * count) of what the real count of the points within the grid polygon should be, and the sum result is equal to the sum * the real count or the (sum * ((count)^1/2)) or the sum times the square root of the count. I can fix the results by adding two extra steps to my process but I don't think I should have to fix basic math errors in MapInfo. When you can't count on the math library functions being written properly what's left?? Has anyone else found this problem? Would there be anyone out there willing to confirm this error with MapInfo 5.5, 6.0, 6.5 to let me know that, for one it's not just me, and that hopefully a newer version has this fixed, if not hopefully MapInfo 7.0 will fix it. If anyone out there would like to help me test this on different version let me know and I can provide you with a more formal description to build test datasets. The tool I use to create the grids is 'gridmake.exe' a great tool for making grids, as it doesn't have the limit on the number of cells it can create as the grid tool that comes with MapInfo. Thanks in advance, Stan Johnston B.Sc. Geologist _______________________________________________________________________ List hosting provided by Directions Magazine | www.directionsmag.com | To unsubscribe, send e-mail to [EMAIL PROTECTED] and put "unsubscribe MapInfo-L" in the message body.
