[mkgmap-dev] DEM: performance with bicubic interpolation

Tue Jan 23 12:59:38 GMT 2018

Hi Andrzej,

I also suggest to make interpolation optional.

So far I don't understand your argument. I agree, compilation time is
not the only criteria. The question is, what is the benefit for the user.
For example: If accuracy of srtm is +- 10m and the difference between
with/without interpolation is +-1m, then it's definitely not worth
spending any effort on interpolation. Only in cases, where interpolation
accuracy is on same level than srtm accuracy, it starting to be worth
spending time for it.

Do you have any values for differences with/without interpolation with
same input data?

Henning

On 23.01.2018 20:22, Andrzej Popowski wrote:
> Hi Gerd,
>
> there are different kind of bicubic interpolations. I'm not good at
> this math, I think the previous version was actually bicubic spline
> interpolation. See other possibilities here:
> http://mrl.nyu.edu/~perlin/cubic/Cubic_java.html
>
> I don't know, which type of spline or cubic interpolation is best for
> DEM. Maybe differences aren't big, but I think it is better to have
> good interpolation than fast one. You compile a map once but then many
> people can use it.
>
> It shouldn't be difficult to include an option like:
> --dem-interp=..
>