Markus Metz wrote: > I think I understand. If the largest values are in the range of 2^6 - > 2^7, the ULP would have a magnitude of 2^-17 ~= 7.629395e-06?
Yes. > I am > asking because lately I observed slightly corrupted vector coordinates > in shapefiles created with recent ESRI software and suspect > float-double conversion artifacts. For latlon coordinates, the largest > values are in the range of 2^6 - 2^8, depending on the longitude. > v.in.ogr could then, based on the largest coordinate values, suggest a > threshold for snapping if topological errors are encountered. If cartographic projections or datum transformations are involved, there are likely to be more significant issues than floating-point rounding errors. The main problem is that, for a non-affine transformation, the transformation of a line between two endpoints isn't the same as the line between the transformed endpoints. So e.g. if you have points A, B, and C, where C lies exactly on the line AB, transforming the points to A', B', and C' typically won't result in C' lying on the line A'B'. -- Glynn Clements <[email protected]> _______________________________________________ grass-dev mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/grass-dev
