Hi,
First, thanks a lot for QlandkarteGT. I'm a very happy user.
I was trying to filter a track so that it would fit under the 500-points
limit of my GPS, but QlandkarteGT was not removing points that could
obviously be removed. So I dug into the code, and found that
in CDlgTrackFilter.cpp, you do:
if (delta < min_distance || (checkAzimuth && AzimuthDelta < minAzimuthDelta))
{
if(deltaEle < 3)
{
trkpt->flags |= CTrack::pt_t::eDeleted;
}
So points are not removed if the elevation change is more than 3 meters.
I have two uses cases for filtering traces:
(A) when trying to fit a trace in my GPS without splitting it, to then use it
in "trackback" mode. In that case, I really don't care about elevation
data, and it could safely be removed.
(B) when trying to clean traces a bit before archiving them. In that case, I
care
more about not losing the total elevation for the track. That means that
points
can be safely removed if they are local minimums or maximums. e.g. if you
have:
A (10m) -- B (15m) -- C (10m) => B shouldn't be removed
A (10m) -- B (15m) -- C (20m) => B could be removed
Finally, I've always found the "Filter track" menu quite unclear. For example,
it's not clear if it should be read as "Hide track points if dist from previous
< 20 meter AND azimuth from prev < 6°", or if it's a OR.
I think that the menu could be improved by stating when points cannot be
removed, using a list of checkboxes:
Hide track points unless:
[X] Distance to previous > 10m
[X] Azimuth from previous > 6°
[X] Time from previous > 5s
[X] Altitude change > 10m
[X] The point is a local minimum or maximum regarding elevation
(of course, the code would do a OR between those settings)
What do you think?
- Lucas
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