Re: [Gpsbabel-misc] looking up (aka inventing) elevations

[Steven E. <ste...@cl...>]

At 07:31 PM 2/8/18, nwastra wrote:
>GPSies https://www.gpsies.com/convert.do can add/replace elevation to a gpx

Have to log in.

At 07:31 PM 2/8/18, nwastra wrote:
>http://www.gpsvisualizer.com/elevation also does the same

Works! One file at a time, but it works! Thanks.

At 10:16 PM 2/8/18, Ralf Horstmann wrote:
>Viking would be another option: https://sourceforge.net/projects/viking/

Hmmm. Another open source tool that I have to learn. And its "ESL" docs.

At 10:54 PM 2/8/18, Robert Lipe wrote:
>Via our Height filter, GPSBabel sort of tries to fake elevation

I keep forgetting that the GUI doesn't present all options. Sigh.
Have I already complained about that??

So I used the command line with "-x height,wgs84tomsl" and it moved my
waypoint from 0m to 32m... while a map shows it should be 511m (in AZ).
Not useful. It's showing the error, not the actual elevation. Does
GPSBabel know about actual elevations?

At 10:54 PM 2/8/18, Robert Lipe wrote:
>Perhaps we add a flag to the height filter that determines if your alt/ele data is just flagrantly bogus

If you're taking requests, add a pair of "fixit" flags that will replace
ALL or just the BAD elevations with something derived from some DEM source.
If you can't fix them, removing suspect elevation tags is the next best
option. Not sure how you'll choose the thresholds, but Mt Everest and the
Marianas Trench represent max and min in some sense!

As you know I still use the .tpo format, and they report unknown elevations
as -999ft in their GUI. How that comes out in the GPX is the matter of some
variation. It might be a VERY large number (over 10km high) or it might be
-1965m (not sure what that means) but there is a small set of error numbers
that I'm already "fixing" by setting to zero or just removing the ele tag.
So *finding* the bad waypoints is easy. Changing them to something *useful*
is harder, but when I do I can just read the GPX back into Topo right on
top of the original data and the waypoints are magically fixed for all time.

My current solution (and really, a big THANKS to all who commented) is to
extract partial GPX files containing only the "bad" waypoints, feed those
to one of the web converters, and feed the result back into Topo to 
selectively update the waypoints I've identified as bad. Might even be
worth tagging the waypoints with filename as a comment and lumping them
all into one GPX for conversion than sorting them back out for import.

Steve