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Topic: BME280 improves GPS? (Read 656 times) previous topic - next topic

george_i

Hi,

I have a BME280 temperature/pressure/humidity sensor and on the product page says that it can improve GPS.

Can anyone explain how is that done?

This is the product page:
http://www.bosch-sensortec.com/de/homepage/products_3/environmental_sensors_1/bme280/bme280_1

wwbrown

The BME280 can help your GPS position solution if used in conjunction with a Kalman Filter or similar.  The reason it can help is the change in altitude measured by the baro pressure sensor on the BME280 will in general more accurate than that measured by the GPS.  GPS gives a lousy altitude reading.

wade

george_i


wwbrown

I should have been a little more helpful than I was.  Your altitude solution will be even better if you have a stationary atmospheric pressure sensor that can measure the the change in barometric pressure in the area you are operating, called the ambient baro pressure.  The change in ambient pressure can be subtracted off the mobile baro sensor operating with the GPS. 

Imagine you are operating a drone for a mission of say 2 hours, the drone starts out at your fixed location and will return there.  The landing will be better if the drone knows how high it is above its landing site.  If you just used the baro sensor on the drone any change in the ambient baro pressure would increase the uncertainty in how high the drone is.  With the baro sensor on the ground station you can compensate for the change in ambient baro pressure. 

The application just described is not really an example of how the baro sesnors can increase the accuracy of the GPS altitude solution, but an example of using two additional sensors to get a much better solution than the GPS could.

I hope I have not confused the issue.
wade

george_i

I think I got it.
I need an altitude reference, which is mean sea level.

Probably each time the device is started, will have to obtain from somewhere the sea level pressure.

But assuming that I have this sensor in my pocket, how can I differentiate if the pressure changed because of the weather, or because I climbed a hill?
Because the altitude shouldn't change if is caused of weather and I'm in same place.

wwbrown

With the sensor in your pocket you can not tell whether a change in pressure is due to the elevation or ambient pressure change.  I believe pilots set their altimeters to the altitude of the airport before departure to remove the bias due to ambient pressure.

george_i

Wikipedia says:
Quote
Because barometric pressure changes with the weather, hikers must periodically re-calibrate their altimeters when they reach a known altitude, such as a trail junction or peak marked on a topographical map.
Airplanes have a different method: link

In my case I will have to calibrate it by obtaining with mobile phone's GPS the altitude, once in a while. For example when the pressure changes more in a shorter time.

Usually changes in temperature and humidity are linked to air pressure, so if these are not changed significantly, I can assume that the altitude changed.
Although is not that simple and I could be wrong.

That's cool :) Makes the project more interesting.

jboyton

#7
Sep 26, 2015, 08:21 pm Last Edit: Sep 26, 2015, 08:23 pm by jboyton
In my case I will have to calibrate it by obtaining with mobile phone's GPS the altitude, once in a while. For example when the pressure changes more in a shorter time.
GPS altitude has a lot of jitter. Here's an example of a short out and back walk with a GPS and a barometric altimeter:




Usually changes in temperature and humidity are linked to air pressure, so if these are not changed significantly, I can assume that the altitude changed.
That would be a faulty assumption.

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