Hi Frank what problem do you see when we interpolate data? What is the advantage of voids? Gerd ________________________________________ Von: mkgmap-dev <mkgmap-dev-bounces@lists.mkgmap.org.uk> im Auftrag von Frank Stinner <frank.stinner@leipzig.de> Gesendet: Mittwoch, 10. Januar 2018 10:53:44 An: mkgmap-dev@lists.mkgmap.org.uk Betreff: Re: [mkgmap-dev] HGT - getElevation() Hi Gerd and Andrzej,
your choice of triangle is arbitrary.
of course, but the version with 4 triangles isn't.
bilinear interpolation seems better
Yes. It's a little bit more to calculate, but better. For our special case it is: h = h11 * (1 + y * x - x - y) + h21 * (x - y * x) + h12 * (y - y * x) + h22 * y * x (h11 is left-bottom in coordinate origin, the horizontal and vertical distance is 1) If your java-class have to much overhead, you can use this formula. By the way, i would be very defensive with interpolation in the case of missing values. The hgt values are only interpolated values from original measurments. I would not interpolate values in the near of missing values. That give us a nice but unreliably picture. Frank