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Topic Date User

Digital SLRs that are GPS capable 28-Sep-2009 At 6:58:58 AM racingtadpole

Message

On 25/09/2009 Richard Delaney wrote:

>GPSin/outboard do not really cut it for environmental field work. How
>do you know what
>accuracy the position fix is? For consumer grade GPS, the position is
>+/- 15m
>assuming you have good sky view. It may be +/- 50m or worse once you
>introduce
>trees/cliffs/buildings etc. All that is recorded with the photo is the
>calculated position
>and no statement of positional confidence.

To take us on a bit of tanget for a little bit. There is no real distinction between Military or Civi GPS units anymore (at least not as far as accuracy of a fix goes). The Gulf war in Kuwait in the early 90's saw to that (the Americans had to put civi units into service because of a lack of military units, to do so they had to turn the encryption that made the civi units less accurate off. It has never been re-instated). I used to have quite a lucrative sideline building differential correction setups for geo exploration teams but there is no need for that now. A Garmin E-trex can provide accuracy to with in 2m with a multi dimensional fix (3d fix) and accuracy to 12m in the event it cant triangulate and makes do with a 2d fix. It would be a very unusual set of circumstances to see accuracy drop to 50m these days. This is why satellite navigators for cars have become the norm now, the cost of the technology has finally caught up with the accuracy of it (if the militray satellites were still encrypted then satnav wouldnt be possible with out the use of differential correction, not hard to do but the cost goes up considerably). Most mobile phones these days can triangulate to within 5 metres just using the working RF carrier and the positions of the towers providing them as an absolute. It is a bit heavy on the bandwith to do it, which is why the carriers that provide it arent shy of charging for it.

Anyway I'll stop babbling on about the pedantic technicalites of it all now...