[mkgmap-dev] DEM: performance with bicubic interpolation

Tue Jan 23 13:09:17 GMT 2018

For srtm I found elevation accuracy of 6m in wikipedia, so my 10m was
not that unrealistic.

Btw. We are talking about interpolating from hgt-data position to
Garmin-data position, aren't we?

For filling voids, it would be a good idea to use some spline
interpolation as written here:
https://en.wikipedia.org/wiki/Shuttle_Radar_Topography_Mission#Void-filled_SRTM_datasets

Henning
*
*
On 23.01.2018 20:59, Henning Scholland wrote:
> 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=..
>>
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