How to Adjust Track Altitude for Google Earth

[RC]

When I export a track & load it in Google Earth, with altitude set to "Relative to Ground" the altitude shown is much too high ( a car ride looks like a flight). This is due to GPS Essentials recording True Altitude (above sea level) while what displays best in Google Earth is Absolute Altitude (altitude above ground level).

If there were a way within GPS Essentials to adjust altitude to the starting point (AGL) and have that be what is imported into Google Earth the problem would be solved, but meanwhile I am looking for another solution.

Here is a sample set of where the altitude data is in the .kml file;

<gx:coord>-85.420044 38.174995 222.8</gx:coord>

<gx:coord>-85.42005 38.174995 222.8</gx:coord>

<gx:coord>-85.42005 38.174995 222.7</gx:coord>

The last  4 digits (i.e. 222.8, 222.7, etc) are the altitude. I have been able to manually adjust this data to the appropriate (Google Earth) altitude, but there are so many data sets in each track that an automated method is needed to make this feasible.

Can anyone offer an automatic way of adjusting this data? Seems like a regular expression in Notepad++ might work, but I don't have the expertise to create it. There may be another way via XML, or some way I haven't thought of?

Any help would be appreciated by myself, and probably useful to many others.

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[Paul Hutchinson]

As long as you aren't actually flying you can do what I do and set the track to Clamped to Ground in Google Earth.

Paul (terrestrial :) Hutch

[RC]

Hi Paul,

Yea, it actually is for low altitude flying, so having the correct altitude relative to the ground would be really nice.

Thanks for trying to help.

I've also tried taking the data into Excel, but the latitude, longitude, and altitude are all in the same 'cell' separated by a space and I'm not sure how or if math operations could be run on them like that.

Seems like there should be a simpler solution.

Thanks again.

More ideas are welcome...anyone?

[Johan Nilsson]

You need a DEM (digital elevation model) over your area to compensate the height. Google Earth are not so precise, which you easily can see if you go the fly-simulator in Google earth.  https://www.youtube.com/watch?v=fVjacZWBrbw Don't think you can import a DEM in GPSE? GPS-altitude are often mean sea-level or ellipsoid i think and are about 10-20m wrong in the area I am in. Also GPS are not so precise in elevation as in log-lat.

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[Michael Schollmeyer]

The GPS elevation alone is not good enough. You can see this when importing a track into Google Earth: It cuts into the surface of the earth sometimes. For devices that feature a pressure sensor, local altitude changes can be more precise, but as long as you don't have a good starting point, your data will be offset by the GPS elevation error. GPS Essentials is also not storing the pressure altitude into KML or GPX.

GPS Essentials does not have a local elevation model, but you can fill in the elevation from one if you have network access. Check out Get Elevation in waypoint view and Fill Elevation in stream view.

Regards, Michael
mictale.com/ms
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> On Nov 5, 2016, at 4:30 AM, Johan Nilsson <joni...@gmail.com> wrote:
>
> You need a DEM (digital elevation model) over your area to compensate the height. Google Earth are not so precise, which you easily can see if you go the fly-simulator in Google earth. https://www.youtube.com/watch?v=fVjacZWBrbw Don't think you can import a DEM in GPSE? GPS-altitude are often mean sea-level or ellipsoid i think and are about 10-20m wrong in the area I am in. Also GPS are not so precise in elevation as in log-lat.
>
> 2016-11-04 16:14 GMT+01:00 RC <rcd....@gmail.com>:
> Hi Paul,
>
> Yea, it actually is for low altitude flying, so having the correct altitude relative to the ground would be really nice.
>
> Thanks for trying to help.
>
> I've also tried taking the data into Excel, but the latitude, longitude, and altitude are all in the same 'cell' separated by a space and I'm not sure how or if math operations could be run on them like that.
>
> Seems like there should be a simpler solution.
>
> Thanks again.
>
> More ideas are welcome...anyone?
>
>
>
>
> --
> You received this message because you are subscribed to the Google Groups "GPS Essentials" group.

> To unsubscribe from this group and stop receiving emails from it, send an email to gpsessential...@googlegroups.com.

> To post to this group, send email to gpsess...@googlegroups.com.
> Visit this group at https://groups.google.com/group/gpsessentials.
> For more options, visit https://groups.google.com/d/optout.
>
>

> --
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[RC]

With my situation, (a situation I share with any low altitude pilots that would like to import tracks into GE), the altitude is just too high. Other than that it would be perfect.

If there were a way to subtract 100m from all points of altitude in a track, either within GPSE or elsewhere, it would be a seamless transfer.

I wonder if it might be possible to have a configurable altitude adjustment in GPSE; just like a regular altimeter.

Otherwise, some automated way to adjust the data after export should be possible for someone who is expert enough in such things.

Still hoping...

On Thursday, November 3, 2016 at 2:58:19 PM UTC-4, RC wrote:

[Michael Schollmeyer]

Both KML and GPX are XML files, so you could run some XSLT on them to convert them and do the transformation. I don't think that's the way to go, though. There is pressure altitude in GPS Essentials anyway, which is adjustable and more accurate within small time windows. The question that I could not answer yet is how to merge the two altitudes to produce something meaningful.

Regards, Michael
mictale.com/ms
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[RC]

The pressure altitude sounds promising with it's adjustability and better precision.

Meanwhile, I did take a shot at modifying the data via Excel formulas, but I don't know how to isolate the altitude. It's grouped with the GPS coordinates.

Does someone know how to apply an Excel formula to the last digits (222.8) in this set? Ideally without breaking the set up?

> <gx:coord>-85.420044 38.174995 222.8</gx:coord>

On Thursday, November 3, 2016 at 2:58:19 PM UTC-4, RC wrote: