GPSID and altitudeWRTSeaLevel in win mobile 6.1

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

Henryk
Mon Jul 07 11:33:01 CDT 2008

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

zdarsky_at_zac_minus_it_dot_de>
Mon Jul 07 13:13:01 CDT 2008

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
>
>

zdarsky_at_zac_minus_it_dot_de>
Mon Jul 07 14:10:00 CDT 2008

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
>
>

Henryk
Mon Jul 07 17:53:13 CDT 2008

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

zdarsky_at_zac_minus_it_dot_de>
Tue Jul 08 01:31:02 CDT 2008

Hello Henryk,

as I wrote in my first posting, the value for the sealevel is always invalid.
But I don't understand your answer.

If it is invalid, I only get the geoid height?
I thought the geoid height is the sealevel.


Currently I can not access the nmea sentence.
The API doesn't deliver it.

Regards



--
Michael Zdarsky



"Henryk Birecki" wrote:

> 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
>
>

Henryk
Tue Jul 08 14:45:34 CDT 2008

Sorry I miss-spoke, in my previous message change last "geoid" to
"ellipsoid". GPS outputs two numbers. Height over MSL (according to
standard) and geoid separation which is the difference between MSL and
ellipsoid heights (I never remember the sign without looking up).
Intermediate driver parses NMEA and provides you validity flags and
computes height over ellipsoid. If the geoid separation is missing it
probably interprets "MSL" altitude as height over ellipsoid and
adjusts flags accordingly. Problem with SiRF2 chips was that they
outputted height over ellipsoid instead of MSL whether or not
separation was present.

Cheers,
Henryk

Michael Zdarsky <zdarsky_at_zac_minus_it_dot_de> wrote:

>Hello Henryk,
>
>as I wrote in my first posting, the value for the sealevel is always invalid.
>But I don't understand your answer.
>
>If it is invalid, I only get the geoid height?
>I thought the geoid height is the sealevel.
>
>
>Currently I can not access the nmea sentence.
>The API doesn't deliver it.
>
>Regards

zdarsky_at_zac_minus_it_dot_de>
Wed Jul 16 06:28:11 CDT 2008

Hello Henryk,

ok, with this correction your answer makes sense.
I think it is a QualComm chipset because AFAIK
the HTC touch diamond uses QuallComm and thus not a SiRF2 chipset.
Correct?

I already wrote 3 mails to HTC concenting this problem. NO ANSWER since 4
weeks.
So may be other take care before buying this device. The support seems to be
very bad.

But to get back to your answer, if the chip isn't delivering the correct data,
it also doesn't makes sense to get down to the nmea sentence, because it
would be wrong too.
Correct?

Thank you for your help.
Michael

--
Michael Zdarsky



"Henryk Birecki" wrote:

> Sorry I miss-spoke, in my previous message change last "geoid" to
> "ellipsoid". GPS outputs two numbers. Height over MSL (according to
> standard) and geoid separation which is the difference between MSL and
> ellipsoid heights (I never remember the sign without looking up).
> Intermediate driver parses NMEA and provides you validity flags and
> computes height over ellipsoid. If the geoid separation is missing it
> probably interprets "MSL" altitude as height over ellipsoid and
> adjusts flags accordingly. Problem with SiRF2 chips was that they
> outputted height over ellipsoid instead of MSL whether or not
> separation was present.
>
> Cheers,
> Henryk
>
> Michael Zdarsky <zdarsky_at_zac_minus_it_dot_de> wrote:
>
> >Hello Henryk,
> >
> >as I wrote in my first posting, the value for the sealevel is always invalid.
> >But I don't understand your answer.
> >
> >If it is invalid, I only get the geoid height?
> >I thought the geoid height is the sealevel.
> >
> >
> >Currently I can not access the nmea sentence.
> >The API doesn't deliver it.
> >
> >Regards
>
>

Henryk
Wed Jul 16 11:04:32 CDT 2008

Michael Zdarsky <zdarsky_at_zac_minus_it_dot_de> wrote:

>Hello Henryk,
>
>ok, with this correction your answer makes sense.
>I think it is a QualComm chipset because AFAIK
>the HTC touch diamond uses QuallComm and thus not a SiRF2 chipset.
>Correct?

I have no idea. You may want to check with QuallComm what their chip
set sends out.

>
>I already wrote 3 mails to HTC concenting this problem. NO ANSWER since 4
>weeks.
>So may be other take care before buying this device. The support seems to be
>very bad.
>
>But to get back to your answer, if the chip isn't delivering the correct data,
>it also doesn't makes sense to get down to the nmea sentence, because it
>would be wrong too.
>Correct?

Yes. My suggestion to look at NMEA was mostly to double check that
nothing else is going wrong.

Cheers,
Henryk