Hi Andrzej, did not try it yet but I think the method fillArray is off by one. Bicubic expects grid [-1,0,1,2] X [-1,0,1,2] fillArray uses [0,1,2,3]X[0,1,2,3] 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