I noticed that this went to me directly, and not to the list. I have
not useful answer here.
Begin forwarded message:
> From: "Bill Monicher" <bmacd5153@...>
> Date: 22 december 2008 00:41:47 GMT+01:00
> To: "Maarten Sneep" <maarten.sneep@...>
> Subject: Re: [Gpsbabel-misc] Realtime tracking altitude value
> consistently low
> More to this than meets the eye.
> I'm sure it is not related to a map, because as I sit here, the
> altitude on the GPS display varies 5 or 6 meters. The displayed value
> correlates well with the value on the topo map. When I connect this
> unit via usb, and use the following command:
> cls & gpsbabel -T -i garmin -f usb: -o xcsv,style=tcapture.style -F
> I get a line similar to this:
> 49° 10' 30.951" N 122° 39' 3.299" W 9.250700951
> 2008-12-21 08:06:51 2008-12-21T08:06:51Z 39803.33809028
> The relevant fields of tcapture.style are:
> IFIELD LAT_HUMAN_READABLE,"","%dø %d' %5.3f" %c"
> IFIELD LON_HUMAN_READABLE,"","%dø %d' %5.3f" %c"
> IFIELD ALT_METERS, "", "%12.9f" #altitude in meters
> IFIELD GMT_TIME, "", "%Y-%m-%d %H:%M:%S"
> IFIELD ISO_TIME, "", "%s"
> IFIELD EXCEL_TIME, "", "%14.8f"
> The altitude displayed on the GPS unit at this time was 26m
> Another program (gpsutility http://www.gpsu.co.uk/) has a GUI that
> shows me that the Altitude is the same as on the display.
> Just now, when I ran it again to be sure, I noticed this line: "Geoid
> sep= 17.4m"
> I ran real-time tracking using
> cls & gpsbabel -T -i garmin -f usb: -o nmea -F out.nmea
> Here is an excerpt from out.nmea:
> In the altitude section of $GPGGA we find:
> According to http://www.gpsinformation.org/dale/nmea.htm#RMC
> the second value is "Height of geoid (mean sea level) above WGS84
> I'm going to assume that the data is there, since the other program
> can read it.
> If that is the case then the Garmin serial/USB protocol might not be
> reading it by design, or it might be mis-handling it.
> My GPS might be doing something non standard too.
> Is there a facility in GPSBabel real time tracking to capture the raw
> output of the connection?
> If so, I might be able to determine if my unit is actually putting out
> the correct information.
> On Sun, Dec 21, 2008 at 1:26 AM, Maarten Sneep <maarten.sneep@...
> > wrote:
>> The only thing I can think of is that the GPS uses information from a
>> map you have loaded to find the local altitude of the geolocation.