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From: Michael Zdarsky on 7 Jul 2008 07:03
Hello,

I am using the GPSID from Windows Mobile 6.1 to avoid the nmea data
manually.

The problem is, when I call the GetPosition API I never get the
altitudeWRTSeaLevel.

It is always invalid.
altitudeWRTElipsoid is valid.

Can somebody explait that?

Is that a driver problem?
Or is it a GPS chip problem?

I am using the HTC Touch Diamond mobile phone.

Any hint would be nice.

Thank you
Michael
--
Michael Zdarsky

From: Henryk Birecki on 7 Jul 2008 12:33
GPS provides (measures) height over ellipsoid. To transform that to
MSL altitude requires a model of earth surface. Not all devices (at
least the ones I dealt with in the past) have that model. If my memory
serves me right, SiRF II devices did not, but I may be wrong. They
certainly output non-standard NMEA sentences.

Cheers,
Henryk

Michael Zdarsky <zdarsky_at_zac_dash_it_dot_com> wrote:

>Hello,
>
>I am using the GPSID from Windows Mobile 6.1 to avoid the nmea data
>manually.
>
>The problem is, when I call the GetPosition API I never get the
>altitudeWRTSeaLevel.
>
>It is always invalid.
>altitudeWRTElipsoid is valid.
>
>Can somebody explait that?
>
>Is that a driver problem?
>Or is it a GPS chip problem?
>
>I am using the HTC Touch Diamond mobile phone.
>
>Any hint would be nice.
>
>Thank you
>Michael

From: Michael Zdarsky on 7 Jul 2008 14:13
Hello Henryk,

thank your for your answer.

AFAIK the HTC device are using QualComm GPS chipsets
and not SiRFs.

Do you know problems with the quallcomm chips?

Regards
Michael
--
Michael Zdarsky



"Henryk Birecki" wrote:

> GPS provides (measures) height over ellipsoid. To transform that to
> MSL altitude requires a model of earth surface. Not all devices (at
> least the ones I dealt with in the past) have that model. If my memory
> serves me right, SiRF II devices did not, but I may be wrong. They
> certainly output non-standard NMEA sentences.
>
> Cheers,
> Henryk
>
> Michael Zdarsky <zdarsky_at_zac_dash_it_dot_com> wrote:
>
> >Hello,
> >
> >I am using the GPSID from Windows Mobile 6.1 to avoid the nmea data
> >manually.
> >
> >The problem is, when I call the GetPosition API I never get the
> >altitudeWRTSeaLevel.
> >
> >It is always invalid.
> >altitudeWRTElipsoid is valid.
> >
> >Can somebody explait that?
> >
> >Is that a driver problem?
> >Or is it a GPS chip problem?
> >
> >I am using the HTC Touch Diamond mobile phone.
> >
> >Any hint would be nice.
> >
> >Thank you
> >Michael
>
>
From: Michael Zdarsky on 7 Jul 2008 15:10
Hello Henryk,

thank you for your answer.

AFAIK HTC has a QualComm chipset and not a SiRF.

Do you know problems with the QualComm Chipset?

Regards
Michael



--
Michael Zdarsky



"Henryk Birecki" wrote:

> GPS provides (measures) height over ellipsoid. To transform that to
> MSL altitude requires a model of earth surface. Not all devices (at
> least the ones I dealt with in the past) have that model. If my memory
> serves me right, SiRF II devices did not, but I may be wrong. They
> certainly output non-standard NMEA sentences.
>
> Cheers,
> Henryk
>
> Michael Zdarsky <zdarsky_at_zac_dash_it_dot_com> wrote:
>
> >Hello,
> >
> >I am using the GPSID from Windows Mobile 6.1 to avoid the nmea data
> >manually.
> >
> >The problem is, when I call the GetPosition API I never get the
> >altitudeWRTSeaLevel.
> >
> >It is always invalid.
> >altitudeWRTElipsoid is valid.
> >
> >Can somebody explait that?
> >
> >Is that a driver problem?
> >Or is it a GPS chip problem?
> >
> >I am using the HTC Touch Diamond mobile phone.
> >
> >Any hint would be nice.
> >
> >Thank you
> >Michael
>
>
From: Henryk Birecki on 7 Jul 2008 18:54
Michael Zdarsky <zdarsky_at_zac_minus_it_dot_de> wrote:

>Hello Henryk,
>
>thank your for your answer.
>
>AFAIK the HTC device are using QualComm GPS chipsets
>and not SiRFs.
>
>Do you know problems with the quallcomm chips?

No, I do not know anything about these. You may want to take a look at
the NMEA sentences they output and "dive into" the GPGGA sentence.
Actually the GetPosition API should have a flag for valid geoid
separation value. If that one is also invalid, then probably all you
are getting from the chipset is the height above geoid.

Cheers,
Henryk

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