Re: [Paparazzi-devel] measuring altitude with pressure/gps

[Kirk Scheper]

Hey Martin,
As far as I know the result in the INS and the ROTORCRAFT_FP messages 
contain the result of the Kalman filter combing the GPS and the Baro 
when using the vertical float filter (vff). When using the extended 
vertical float filter (vff_entended), the baro offset is estimated 
(using the gps and/or sonar if active).

Without any additional information, I am not sure what you are referring 
to with 'the difference between the GPS and the other parameters is 
generally increasing with height', so I can't help you there.

Please note that you have to define INS_USE_GPS_ALT in your airframe for 
it to be considered in the filter. Additionally, consider the values for 
INS_VFF_R_GPS and VFF_MEAS_NOISE as they will change the noise model 
used for the GPS and baro respectfully, changing the confidence on each 
parameter in the filter.

From what you described, I would have to guess you didn't define 
INS_USE_GPS_ALT so the GPS is not being used in the vertical filter.

I noticed that INS_USE_GPS_ALT and INS_USE_GPS_ALT_SPEED are not 
mentioned in the documentation for the INS so I will update this at my 
next opportunity.

Yours,
Kirk

On 20/08/18 10:28, Martin Mueller wrote:
> Hi,
>
> we are looking into meteo data that we collected using Parrot Bebop2 and were 
> wondering if there is an altitude parameter which is already kalman filtered 
> based on GPS and pressure measurements. So far we have been relying on the 
> ROTORCRAFT_FP:up parameter and applied a linear detrending routine to bring the 
> start and landing altitude to 0m (accounting to pressure changes).
>
> However we just realized that the difference between the GPS and the other 
> parameters is generally increasing with height so we wonder a bit whether the 
> other parameters are purely pressure based and there is a problem with the 
> hydrostatic equation. Maybe the assumed temperature profile doesn't fit the 
> conditions we were facing (much colder), but we are not sure how much of an 
> error to expect from this.
>
> We are generally wondering if there is one parameter that is already kalman 
> filtered. It doesn't look like it since ROTORCRAFT_FP and INS are almost 
> identical (except for the sign convention and sampling rate) and look very 
> similar to the AIR_DATA:amsl_baro (seems to be pressure based). None of them 
> has features like the jumps one can see in the GPS data.
>
> Can we use the paparazzi Kalman filter to easily postprocess a "fused" altitude 
> from GPS and pressure?
>
> Martin
>
> _______________________________________________
> Paparazzi-devel mailing list
> address@hidden
> https://lists.nongnu.org/mailman/listinfo/paparazzi-devel