[clug] GPS, GIS, GTS, SDI and FOSS

[Scott Ferguson]

On 03/03/11 07:21, Brad Hards wrote:
> On Thursday, March 03, 2011 12:27:51 am Scott Ferguson wrote:
>> * Another solution to ionospheric distortion is internet sourced
>> corrective data - any suggestions/experience there?
>> A local base station is unlikely to work due to the local topography.
> I wouldn't have expected that there would be much variation in ionospheric 
> delay across the ACT (or anywhere roughly north / south). The variation is 
> strongest at dawn / dusk. Can you just put something on the roof?
> 
> Brad
> 
> 

Even that tiny variation adds significant error. The best non-military
GPS systems on the market cannot achieve less than 10m absolute accuracy
without corrective data. I can't quickly locate the figures - but after
local signal reflections the largest error factor is ionospheric
distortion (40%?). Of course the DSE sales rep will disagree with me... :-)

I was probably (late night post) a little unclear - my requirements are
for reproducible 1/2 meter to 1 metre absolute accuracy in the ACT with
sub-2 minute warm starts at less than $1K per unit.

http://en.wikipedia.org/wiki/Error_analysis_for_the_Global_Positioning_System#Atmospheric_effects

Not sure what you mean by "put something on the roof"... antennae?  If
so it is a means of reducing signal reflection - doesn't correct for
lens effects.

I'm happy to discuss this further, time allowing, especially as it is a
learning curve for me, but probably best either off-list or under an
[OT] prefaced subject-line (lest I become a hypocrite!)

Cheers