Altitude gain correction
I'm not sure I have fully understood how altitude correction filter works but I experience some troubles with it. I use a device with no pressure sensor, so the only data are from GPS and SRTM1 dem files. I tried with GPS only data and GPS corrected by SRTM without experiencing significant difference. I have set filter to medium. Sometimes saved altitude gain is quite reasonable as expected, some other times it's very high compared to the expected value (also about 2 times the expected value). Also, when planning with Brouter a 80km long trip, I got a altitude gain of about 2600 m while it should reasonably be between 1000-1200 m. This is probably caused by approximation between SRTM1 and Brouter map vector segments. I don't know if your filter works also with planned routes or only with registered tracks. If not, it could be a good idea to implement it.
I also wonder if it could be a good idea to let applying filter manually after the track (or planned route) is saved. I mean: 1) user sets the level of filter impact (low, medium, high,extra high); 2) then he pushes a button and sees results; 3) if result is satisfactory, he saves again (overwriting or duplicating), otherwise tries another filter level or aborts. What do you think?
Would you also explain the principle of the filter algorithm. Is it somehow averaging close points' altitude or taking one waypoint every a number?