Hi Andrzej, I'll try this on monday, Maybe you can create a 2nd branch so that others can try the different results? BTW: I think that the calculation of qx and qy for the interpolation should be changed. The current code in 4071 adds up rounding errors when data for the upper right area is calculated in a large tile spanning multiple degrees. I am working on that. Gerd ________________________________________ Von: mkgmap-dev <mkgmap-dev-bounces@lists.mkgmap.org.uk> im Auftrag von Andrzej Popowski <popej@poczta.onet.pl> Gesendet: Samstag, 20. Januar 2018 00:50:19 An: mkgmap-dev@lists.mkgmap.org.uk Betreff: Re: [mkgmap-dev] HGT - getElevation() Hi Gerd, I have included bicubic interpolation created by Ken Perlin: https://github.com/mlevans/pretty-heatmaps/blob/master/DensityArrayCreation/... Bicubic interpolation is used only for layers with good resolution (3 arc seconds or better). For other cases bilinear interpolation is used. Patch is attached. -- Best regards, Andrzej