[pct-l] Follow-up to the earlier GPS discussion

[Bill Burge]

Your Z axis calc angle issue is correct.

Bill Burge
Typoed on my iPhone!

On May 19, 2010, at 7:39 PM, Carl Siechert <carlito at gmail.com> wrote:

> I don't get this. Putting aside my question about how gravity is
> mapped...Where is this elevation mapping data stored? In the  
> receiver? And
> with all the other mapping minutiae stored in most receivers, why  
> can't the
> elevation be more accurate? Btw, in limited observations with  
> automotive
> receivers, I haven't noticed that elevations on a (presumably  
> economically
> justifiable) interstate highway are any more accurate than those  
> seen far
> afield.
>
> I always assumed that vertical position was calculated on the fly by
> triangulation, just like lat/long. And I further assumed that the  
> reason for
> the usual error is simply that the high angle of the satellite signals
> doesn't allow for as much precision when triangulating on the Z- 
> axis. Am I
> lost?
>
> On Wed, May 19, 2010 at 2:44 PM, <gwschenk at socal.rr.com> wrote:
>
>>
>> Vertical position is based on mapping of the earth's gravity. This  
>> mapping
>> is densified in more urban areas where it is economically  
>> justified. In
>> remote mountain regions it is not considered as important. And so,  
>> every so
>> often you will read where someone will complain that the elevation of
>> Whitney is wrong, because his Magellan says so!
>>
>>
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