Re: [Qlandkartegt-users] Feature request: DEM profile interpolation
Am Mon, 24. Jul 2017 um 21:28:42 +0200 schrieb Oliver Eichler: Hi Oliver, > There is no chance for an algorithm to know what points to use for the linear > interpolation interval. Without knowing the properties of the terrain, > knowing > that there is a valley floor, that point A and B are good ones and that the > terrain can be represented by a line, it's impossible to define the intervals > used for interpolation. I cannot believe that. Assuming two points A(valley) and B(pass) on a freshly routed track which are specified by their data A(long, lat, height) and B(long, lat, height). The long and lat data are available from the track itself as well as the points of the course in between. The height is available from DEM. So now we can calculate the total height difference = height(B) - height(A) To calculate the inclination we need the length of the track between A and B. This is just the sum of all distances between the track points. Now we can calculate the inclination = height/length for the selected track section. For each track point between A and B we now can assign the interpolated height(point) = inclination * distance(A, point). Remark: distance(A, point) is of course the cumulated distance over each track point between A and the target point. Guido -- http://wie-im-flug.net/ http://www.lug-burghausen.org/ signature.asc Description: PGP signature -- Check out the vibrant tech community on one of the world's most engaging tech sites, Slashdot.org! http://sdm.link/slashdot___ Qlandkartegt-users mailing list Qlandkartegt-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/qlandkartegt-users
Re: [Qlandkartegt-users] Feature request: DEM profile interpolation
There is no chance for an algorithm to know what points to use for the linear interpolation interval. Without knowing the properties of the terrain, knowing that there is a valley floor, that point A and B are good ones and that the terrain can be represented by a line, it's impossible to define the intervals used for interpolation. In such a case you have to draw a very coarse track with just a few points at very well defined points. This will give you a rough estimate about the ascent and descent. The distance will be wrong of course. The core problem is the bad DEM data. It lacks the information needed. There is no way to create better information out of such data without having another source of information to correlate with. Am Montag, 24. Juli 2017, 21:14:43 CEST schrieb Guido Scholz: > Am Mon, 24. Jul 2017 um 20:30:08 +0200 schrieb Oliver Eichler: > > Hi Guido, > > Hi Oliver, > > > I do not understand why the elevation filter "Interpolate Elevation Data" > > with setting "coars" does not fit your need. The used spline > > interpolation is much more natural than a linear interpolation. > > yes and no. The spline interpolation provides no chance for improvement > for very narrow valley situations like in the attached graph. The plot > around 15 km +-3 km in reality is at 2150 m (Río Marañon valley). A > linear interpolation would give a chance to eliminate this error (more > than 200 m!) completely. > > > But either linear or spline interpolation will not provide good results if > > your input data is faulty. Especially along steep walls a few meters > > deviation in the horizontal plain can result in a significant difference > > of the elevation. In that case you have to reduce points to a minimum. > > And fine tune the position to a better fit. > > Yes that is clear but this is no solution for narrow valleys where DEM > data gets wrong due to its "natural" behavior. > > The linear interpolation would just be a tool to make elevation gain > calculation much easier. It would also help in your case of a not so > precisely painted route. > > Guido -- Check out the vibrant tech community on one of the world's most engaging tech sites, Slashdot.org! http://sdm.link/slashdot ___ Qlandkartegt-users mailing list Qlandkartegt-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/qlandkartegt-users
Re: [Qlandkartegt-users] Feature request: DEM profile interpolation
Am Mon, 24. Jul 2017 um 20:30:08 +0200 schrieb Oliver Eichler: > Hi Guido, Hi Oliver, > I do not understand why the elevation filter "Interpolate Elevation Data" > with > setting "coars" does not fit your need. The used spline interpolation is much > more natural than a linear interpolation. yes and no. The spline interpolation provides no chance for improvement for very narrow valley situations like in the attached graph. The plot around 15 km +-3 km in reality is at 2150 m (Río Marañon valley). A linear interpolation would give a chance to eliminate this error (more than 200 m!) completely. > But either linear or spline interpolation will not provide good results if > your input data is faulty. Especially along steep walls a few meters > deviation > in the horizontal plain can result in a significant difference of the > elevation. In that case you have to reduce points to a minimum. And fine tune > the position to a better fit. Yes that is clear but this is no solution for narrow valleys where DEM data gets wrong due to its "natural" behavior. The linear interpolation would just be a tool to make elevation gain calculation much easier. It would also help in your case of a not so precisely painted route. Guido -- http://wie-im-flug.net/ http://www.lug-burghausen.org/ signature.asc Description: PGP signature -- Check out the vibrant tech community on one of the world's most engaging tech sites, Slashdot.org! http://sdm.link/slashdot___ Qlandkartegt-users mailing list Qlandkartegt-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/qlandkartegt-users
Re: [Qlandkartegt-users] Feature request: DEM profile interpolation
Hi Guido, I do not understand why the elevation filter "Interpolate Elevation Data" with setting "coars" does not fit your need. The used spline interpolation is much more natural than a linear interpolation. But either linear or spline interpolation will not provide good results if your input data is faulty. Especially along steep walls a few meters deviation in the horizontal plain can result in a significant difference of the elevation. In that case you have to reduce points to a minimum. And fine tune the position to a better fit. Oliver Am Montag, 24. Juli 2017, 19:52:27 CEST schrieb Guido Scholz: > Dear developers, > I like to request a new feature to improve elevation profile editing for > planned routes. As mentioned in my earlier request today DEM elevation > data shows a wobbling effect if available only in low resolution for > mountainous areas. In certain regions of the earth, like southamerica, > currently it is a pretty standard to have for example only 90 m > resolution. But also 40 m resolution can lead to this wobbling effect in > mountainous regions like the Andes. > > For planning routes this is not just a cosmetic issue but results in > significant error for summing up the elevation gain for one trip. As I > found planning my last years trip to Peru the error can easily sum up to > 50 % or even much more. This is caused by the continuous up an down while > in reality the road may have a countinuous inclination. Ofcourse the > situation did not improve for my this years planning ;-). > > To ease planning I like to have a new feature in the "filter" section > under the topic "Change elevation of track points". There currently are > some options available but these are unsufficient regarding the > described usecase. > > My proposal is to add a new linear interpolation option to take the > start and the end of a marked range and do a straight away linear > interpolation between these two points. So for planning a user could > for example start the marked range at a point in the valley and end at a > pass. The resulting error will be significantly lower than the DEM-only > solution (even if smoothing is applied). > > Guido -- Check out the vibrant tech community on one of the world's most engaging tech sites, Slashdot.org! http://sdm.link/slashdot ___ Qlandkartegt-users mailing list Qlandkartegt-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/qlandkartegt-users
