Hi Henning, hgt files contain voids, and we don't write 0 height for such a void, instead we write a value that is considered to be invalid. When you hover over such a point MapSource doesn't display a height. I did not yet try to find out how this influences the ele values in calculated gpx tracks. I assume that a gpx point without ele attribute is created. Gerd ________________________________________ Von: mkgmap-dev <mkgmap-dev-bounces@lists.mkgmap.org.uk> im Auftrag von Henning Scholland <osm@hscholland.de> Gesendet: Mittwoch, 10. Januar 2018 13:48:11 An: mkgmap-dev@lists.mkgmap.org.uk Betreff: Re: [mkgmap-dev] HGT - getElevation() On 10.01.2018 20:33, Andrzej Popowski wrote:
i would be very defensive with interpolation in the case of missing values.
I got the same feeling. The best way to fill voids is to process whole HGT. And I believe that DEM providers already have done it, so any attempt at simple extrapolation would rather add errors than make output better. In my code I preserve voids. If requested coordinates are near void HGT node, then returned value is void.
Hi Andrzej,
From user perspective, I think it's more correct to somehow fill voids based of surrounding data than using elevation = 0. Elevation=0 I would only use as a fall back, if whole hgt-file is missing. I agree with you, that we shouldn't spent a lot of code for guessing.
To have a simple example: If there would be a cone-shape mountain in reality, but in DEM the top of the cone is missing, I would suggest to fill the hole with same elevation as the highest circle. So result in DEM would be a truncated cone shape. Of course reality is not that simple. :'( ;-) Henning _______________________________________________ mkgmap-dev mailing list mkgmap-dev@lists.mkgmap.org.uk http://www.mkgmap.org.uk/mailman/listinfo/mkgmap-dev