Measuring Altitude

Uwe · January 22, 2015, 10:43:31 AM

Hi,

I was using Garmin devices for several years. But now, I gave Oruxmaps on my Mobile Phone (Samsung Note3) a try... and I am really surprised! After some hours reading and testing, I am able to use it now. I am using it for hiking and for mountain biking and in conjunction with the OpenAndroMaps, it fits all my needs.

But I have a question about measuring altitude. With my Garmin, I calibrated the barometric Altitude before each action. And as I understood, Garmin has a built in algorithm, wich keeps the barometric calibration up to date, using the GPS altitude. Even when the weather changes, I got alwas very accurate data. Especially I am interested in elevation gain.

How does it work with Oruxmaps? I couldn't find any information, if there is a automated recalibration of the barometric sensor over time after selecting "Use barometric sensor". Or does Oruxmaps in this setting rely only of the barometric sensor?

Than I choosed to "DEM" and I got much too high elevation gain data.

Now I am fiddeling around with several settings, to find out, what works for me... Worst case is, to use barometric altitude and calibrate manually from time to time during my trip, if I see very accurate GPS readings.

I would be very happy, if someone can answer my question, if there is a built in algorithm, which keeps the barometric sensor calibrated over time or not.

Yours sincerely

Uwe

orux · January 22, 2015, 05:24:55 PM

~~Quote from: "Uwe"~~Hi,

I was using Garmin devices for several years. But now, I gave Oruxmaps on my Mobile Phone (Samsung Note3) a try... and I am really surprised! After some hours reading and testing, I am able to use it now. I am using it for hiking and for mountain biking and in conjunction with the OpenAndroMaps, it fits all my needs.

But I have a question about measuring altitude. With my Garmin, I calibrated the barometric Altitude before each action. And as I understood, Garmin has a built in algorithm, wich keeps the barometric calibration up to date, using the GPS altitude. Even when the weather changes, I got alwas very accurate data. Especially I am interested in elevation gain.

How does it work with Oruxmaps? I couldn't find any information, if there is a automated recalibration of the barometric sensor over time after selecting "Use barometric sensor". Or does Oruxmaps in this setting rely only of the barometric sensor?

Than I choosed to "DEM" and I got much too high elevation gain data.

Now I am fiddeling around with several settings, to find out, what works for me... Worst case is, to use barometric altitude and calibrate manually from time to time during my trip, if I see very accurate GPS readings.

I would be very happy, if someone can answer my question, if there is a built in algorithm, which keeps the barometric sensor calibrated over time or not.

Yours sincerely

Uwe

Hi, Uwe,

Currently there are no automatic procedure; if you make a very long walk, you have to recalibrate the barometer manually during the tour.

Later I will try to include an algorithm that uses the DEM files, or GPS, to do it automatically.

orux

Uwe · January 22, 2015, 06:43:44 PM

Hi Orux,

thank you very much for your fast answer and for your awesome software!

Ok, I look forward for the implementation of the automated barometer calibration feature. In the meantime, I will test DEM-Altitude and manual calibration...

Uwe

dasorsan · January 22, 2015, 11:11:38 PM

I dont know if im doing something wrong, but with GPS OFF i cant have barometric altitude and isnt possible to calibrate it with a known possition. What i've understood is we have dem altitudes and gps/barometric (only one of these) altitudes. But i dont understand why is necesary turn gps on to use barometric altitude or calibrate it. Barometric altitude should work with gps off, should'nt it?

in sensors>gps settings we can toggle between baro altitude/dem altitude/gps altitude but, on the other hand, we have an independent dem altitude button to put in information panel. Im confussed.

Uwe · January 23, 2015, 09:34:31 AM

Hi Darsosan,

it`s here the same and you do nothing wrong ;-)

@all:

And I have one more question: is there a data-field, which displays "Barometric Altitude"? Monitoring GPS-, DEM- and Barometric-data would archieve more transparence. Especially, if the "Auto-Calibration" would have been calibrated...

Uwe

http://www.dl4ac.de">www.dl4ac.de

dasorsan · January 23, 2015, 12:54:16 PM

I think it works like this: we can have 2 independents altitude fields: dem altitude (showed with D in the mountain icon) and just altitude (mountain icon without D), and this one can be set to gps/baro/dem altitude from sensors>gps settings (i suposse that unchecking dem and baro altitudes means activating gps altitude). But its strange, because if I have in screen both data fields, dem altitude and just altitude set to dem, they are not always displaying the same value.

I can see an option to autocalibrate barometer, isn't this what you are looking for, Uwe?

6745th@web.de · January 23, 2015, 02:32:01 PM

The altitude with the D shows the altitude of the map center. If you scroll the map, you see the value is changing. The altitude without the D shows the altitude(gps,DEM,baro) of you're real position. It is good to have both. E.g. I see I am currently at 100m, then I move the map to my target and see the target altitude 400m. So I have to climb 300m

So the D altitude is independent of the gps, it depends of the map position.

I think there is no way to display barometric altitude without gps inside Orux.

z3us · January 23, 2015, 03:20:27 PM

At this point I would suggest a feature: when you move the map, it shows the distance from your current position to the center of the map. What if it also showed the difference of altitudes?

6745th@web.de · January 23, 2015, 03:31:38 PM

Good idea!

Uwe · February 19, 2015, 10:26:24 AM

Hello,

as I said, I need a quite exact measurement of Altitude-Gain. The DEM-Altitude seems to get the height quite good, but there are a lot of little virtual steps. All this little steps are accumulated to the Altitude-Gain and this is the cause of the much to high measurement in this mode. You can see this in the statistic-graph. If I use Barometric-Altitude, the result is much better... but only if there is no significant change of weather (barometric pressure). The most exactly way to evaluate Altitude-Gain is, to recalibrate the barometric-sensor from time to time. The algorithmus has to look, if the difference between barometric- and DEM-Altitude changes. If it does, the barometric sensor has to be recalibrated and the error caused by weather-change of pressure has to be corrected in the Altitude-Gain. Of course it is a little bit complexer, as I described. There has to be a threshold defined and the values have to be averaged.

A second approach could be, to eleminate the little steps of the DEM-Values. DEM-Interpolating set to ON doesn't do the job. Maybe simple averaging can help!?

I know, that this is not a simple task... But especially for hikers and mountainbikers the Altitude-Gain is a very important value.

As I mentioned above, I switched from Garmin to Oruxmaps... and after a lot of testing and learning, I am quite satisfied with OM... only this last point brings me back to Garmin :-(

Uwe

http://www.dl4ac.de">www.dl4ac.de

orux · February 24, 2015, 04:23:16 PM

~~Quote from: "Uwe"~~Hello,

as I said, I need a quite exact measurement of Altitude-Gain. The DEM-Altitude seems to get the height quite good, but there are a lot of little virtual steps. All this little steps are accumulated to the Altitude-Gain and this is the cause of the much to high measurement in this mode. You can see this in the statistic-graph. If I use Barometric-Altitude, the result is much better... but only if there is no significant change of weather (barometric pressure). The most exactly way to evaluate Altitude-Gain is, to recalibrate the barometric-sensor from time to time. The algorithmus has to look, if the difference between barometric- and DEM-Altitude changes. If it does, the barometric sensor has to be recalibrated and the error caused by weather-change of pressure has to be corrected in the Altitude-Gain. Of course it is a little bit complexer, as I described. There has to be a threshold defined and the values have to be averaged.

A second approach could be, to eleminate the little steps of the DEM-Values. DEM-Interpolating set to ON doesn't do the job. Maybe simple averaging can help!?

I know, that this is not a simple task... But especially for hikers and mountainbikers the Altitude-Gain is a very important value.

As I mentioned above, I switched from Garmin to Oruxmaps... and after a lot of testing and learning, I am quite satisfied with OM... only this last point brings me back to Garmin :-(

Uwe

http://www.dl4ac.de">http://www.dl4ac.de

Hi,

if you test the last beta version that you can find in the forum, you will find automatic barometer calibration, both with DEM or GPS.

orux

Uwe · March 02, 2015, 09:05:53 PM

Hi Orux,

again thank you very much for this awesome service!!!!

I just installed the new Beta6.4beta6 and I will test it as soon as possible.

Uwe

Holton181 · March 09, 2015, 10:34:46 AM

@Uwe

From what I have learned so far about digital barometer altimeters is that to get a correct altitude, at least the temperature has to be taken into account. Also for the altitude gain!

The behavior of the pressure in relation to altitude actually highly depend on temperature.

Depending on the temperature you might have gained actual altitude of say 100m, while your barometric altimeter tell you you gained 120m or 80m.

If I'm not mistaking, oruxmaps uses what is called QNH for the altitude calculations not needing the temperature, but to get correct altitude for hiking one needs to use QFF and AT LEAST temperature to calculate it.

If you do not know what QNH and QFF is, google it. But in short:

QNH and QFF are doth the barometric pressure mathematically reduced to sea level.

QNH uses a standard, theoretical atmosphere adopted for the aviation industry. The barometric altimeter in all aircrafts are calibrated to the same standard, theoretical atmosphere. So the QNH provides means for pilots and air traffic controllers in a limited region to know the RELATIVE altitude of each other and avoid collisions. The altitudes on a aircrafts altimeter isn't the EXACT altitude, no barometers using the QNH will give the EXACT altitude, except maybe at the known altitude you calibrating it.

QFF are more used in metrology. To calculate QFF the real, local atmosphere are used, including temperature. It also takes the latitude and the local gravitational constant in to consideration (and maybe other things like humidity). Several different formulas exists for QFF, but to get fairly accurate altitudes one can use a formula only utilizing the temperature and latitude.

If exact altitude gain is important for you, your garmin might give you the best values, depending on how it's derived.

A good QFE-QNH-QFF calculator:

http://www.metpodengineering.com/qfe---qnh---qff-calculator.html">http://www.metpodengineering.com/qfe--- ... lator.html">http://www.metpodengineering.com/qfe---qnh---qff-calculator.html

I am far from professional in thees matters, so if I'm wrong please correct me.

rvb · March 13, 2015, 01:37:41 PM

In aviation RA (radio altitude) is used, for your level above the ground.

Exact height in meters is impossible with one gps in a handy and not very usefull.

The GPS altitude is terribly inaccurate for relatively cheap GPS receivers. Here is an article on that: http://gpsinformation.net/main/altitude.htm">http://gpsinformation.net/main/altitude.htm. One method to cope with this kind of inaccuracy is to filter the altitude data. I used a circular array data structure to remember the last few (I used 4) altitude readings and compute the average. This sufficed to get a relatively accurate reading of vertical speed for my application.

Uwe · March 22, 2015, 04:46:57 PM

@ Holton: yes, what you are saying is my understanding as well. My Samsung Note3 has a temperature compensated barometric sensor installed. This setup is compareable to the Garmin-Setup... only the software makes the difference. A rule of thumb is, to multiply the horizontal error by three, to get the altitude error. When I used my Garmin, I always had to calibrate my baromtric Altitude and Garmin developed a algorythmic, which separates the difference caused by weather changes. That worked really good...

@ Orux: the automatic barometer calibrations works for me! Thank you! I would be happy, if you could explain, how does it work. Does it only once at track start a calibration, or is it active during the hole day?

Uwe