Auto-calibraition of barometric altidude when starting track recording

[shushuk]

Hi,
I have already posted this question in the german section, but maybe I get more response here.

I have a Smartphone with a barometric sensor and would like to use it for altitude measurement on MTB-tours.

As most of the tours start at home and therefore at the same altitude it would be great to have an automatic calibration of the altitude on the specified value ("Höhen Manager" (Hight Manager?) --> "Luftdruck" (Air Pressure?)) when starting to record a track!
As I understand it I have to calibrate the altitude manually every time in advance an then start the record.
Is this correct?!

Cheers
shushuk

[tommi]

Isn't
Altitude manager->Settings->Pressure Sensor = on
+
Altitude manager->Pressur->Automatic = on
enough?
I have these settings since ages and think I always get the correct altitude at the starting point

[shushuk]

Altitude Manager --> Pressure --> Automatic uses GPS-Data to calibrate the altitude, which can be quite wrong as we know. It also does some recalibration every 2 hours.
No, I would like to use my known altitude when starting a track recording.

Current Situation:
Altitude Manager --> Settings --> Pressure Sensor = on
Altitude Manager --> Pressure --> Altitude = 452m (= my known altitude)

After confirmation of the settings the altitude is calibrated to 452m. OK
I start a track recording (in this case immediately after setting the value), the altitude starts at 452m. OK

When stopping the record there are two possibilities:
a. My training was a round trip and I finish at the starting point again, but altitude is not 452 any more but let's say 464m (due to pressure changes f.e.).
b. my training finishes at another point (let's say 680m), transportation back home by car or train

In both cases a track record the next day would start at a wrong value. I would have to start altitude manager again, calibrate the altitude to 452m and start recording.

A setting would be great where you could tell Locus to make an automatic calibration  to the altitude value in altitude manager every time you start a track recording!

Hope I could make my point,
cheers,
shushuk

[tommi]

@shushuk: taken from manual: "Automatic - Locus Map uses GPS altitude or SRTM files altitude and current barometric pressure as basic values and relates all other measurements to these values."

Question now is, what means "or" in this context

[shushuk]

I did a little test today. Setting as recommended:
Pressure-Sensor = on (of course)
Pressure = Automatic

SRTM data is stored on my device for this spesific area.

I started Locus and track recording (via widget). Altitude obviousely was driven from GPS-data (it was different from SRTM value which is shown in map-center...) and far too low. (~360m instead of 450)
Immediately, as GPS-Signal got better, altitude began to rise. After about 30seconds I had an (GPS-)altitude of ~400m.
Therefore I made about 40m uphill, which is Nonsens as I didn't move uphill.
I stopped the test, because this setting is not useful for me.

Then I manually calibrated the altitude to the desired 450m, started a track recording again and everything was perfect. Altitude changes were realistic, just as I expected them.

Only thing is that I would have to do this Manual calibration every time Prior to track recording!

An automatic calibration to the specified value would make an air-pressure-sensor much more usefull!
No GPS-data, no SRTM-data, just the most reliable air-pressure data at track recording...

shushuk

[tommi]

An automatic calibration to the specified value would make an air-pressure-sensor much more usefull!
No GPS-data, no SRTM-data, just the most reliable air-pressure data at track recording...

Well, of course this might the most accurate start setting for altitude in case one knows the exact altitude at the location.
But I personally prefer calibration according SRTM data because this is not too bad in most cases (I know there are examples with quite high difference compared to actual altitude) and works everywhere I start track recording.

And for me this seems to work because I checked some tracks starting from my house and they all start with 473m which is the SRTM value Locus reports for this location. I have no calibration data entered myself.

@Menion: could you shade some light how this automatic calibration really works in case SRTM data for the area is available?

[shushuk]

But I personally prefer calibration according SRTM data because this is not too bad in most cases (I know there are examples with quite high difference compared to actual altitude) and works everywhere I start track recording.

So the "Automatic" Setting is perfect for you.
But it's not useful if you want to focus on air pressure sensor, as I do.

And for me this seems to work because I checked some tracks starting from my house and they all start with 473m which is the SRTM value Locus reports for this location. I have no calibration data entered myself.

I checked it again today, first value was 276m (instead of 450) today, rising as gps-signal got better. So nearly 200m uphill without moving... SRTM value also available for my Location.

Thinking about it I would even recommend not only to automatically calibrate the altitude at the beginning of a track-recording but even at activating of GPS, when AltitudeManager-->AirPressure-->Altitude[value] is set!
It's up to the user which settings and sensors to choose, but if you want to use the air-pressure-sensor and you want to calibrate altitude to a known value, it should be done by the app without additional clicks.

shushuk

[shushuk]

I also posted this topic as an idea at the Locus Help portal about a week ago. Here is the link:
http://help.locusmap.eu/topic/air-pressure-calibration

@Menion: Is this topic on your "radar"? Any comment on that would be appreciated....

Regards
shushuk

[Menion]

Hi, together with new topic on help desk, it's quite a lot of text to read. So i know about this topic, but I've not yet found enough time to deal with it, sorry