View Full Version : Shiny new toy - GPS
craigdiver
20-11-06, 23:26
Hi folks,
Firstly I would like to explain that I regularly get slagged for my inability to find dive sites and usually end up diving some exciting muddy slope!
For my xmas (have it already!) I have a new mobile which has sat nav and a nice sensitinve GPS receiver built-in. I know these sat nav things are quite common now and are probably the best tool available for locating the exact spot to park to access a dive site.
When anybody visits a shore diving site, can we start building up a list of accurate coordinates (I know many site descriptions contain them already - however, would be useful for at least one person to verify them - and a description of the coordinates i.e. park here!)
Am I covering old ground or is this a good idea?
Please post any know coordinates for shore dives on this thread - Thanks;)
Regards
CraigDiver
craigdiver
20-11-06, 23:29
Lat: 56:16:43N
Lon: 002:35:14W
alexmaclennan
21-11-06, 00:13
Craig,
I don't think so...............
I can get 3 different GPS coordinates for any divesite:
1. from my car's satnav
2. from my handheld GPS
3. from my RYA CD admiralty charts
They never tie up :( . In fact they are misleading.
The best way to find a divesite location site is by an accurate distance from a known and unambiguous site eg 6.8 miles past the B8000 turnoff. I think the 'How to get there' bit of each divesite description is by far the most important bit of info.
alex
Lizardland
21-11-06, 00:44
I agree Alex. I've got a GPS receiver on a PDA and another on my laptop, they do vary a bit. There can also be quite a big error when you compare them with OS maps (both units can overlay OS maps on the GPS track).
I wonder if the age of a unit can make a difference? Most GPS's display WGS84 and that co-ordinate system can drift a fair bit over time. Maybe it's because the origins are referring to a different spot? I seem to remember that WGS84 will cease to be accurate in something like 2010. A fix taken in 1996 will be noticeably different to a fix taken on the same point today.
I used to work as a surveyor in the mid 90's. It was even worse then as the US could control the GPS accuracy depending on the mood of their military. We had some surveys go crazy when North Korea was getting agressive (think it was 94) and the US encrypted the signals without warning one afternoon.
With a bit of practice most people can fix a point with a compass and OS map fairly accurately. And distances from a known point is very hard to get wrong.
Cheers,
Stuart
Yep a dive site will always be a set distance from a set point and not vary like GPS. But GPS is good for someone who does not know the area to give a rough idea. And like all technology it will get beter and more accurate....
Lizardland
21-11-06, 12:37
Yep a dive site will always be a set distance from a set point and not vary like GPS. But GPS is good for someone who does not know the area to give a rough idea. And like all technology it will get beter and more accurate....
GPS is very accurate at the moment. The problem is the software that interprets it. The WGS84 model is incredibly complicated (something like 1,000,000 terms in it) and it's replacement is even more complex.
On the other hand, an OS map and driving directions are pretty straightforward :)
I've been involved in compilation of a French dive site database for the last five years. I've never been asked to provide GPS co-ords, if I ever get any questions then they always ask for physical directions.
Thats prob why my wee Garmin takes me back to the same place and a diff GPS doesn't seam to be as accurate. Could it be the software? anyway everyone has a GPS now so they will get more accurate and read the same in time...
Lizardland
21-11-06, 13:36
Just a thought when leaving your car while diving with a Sat Nav unit in it... don't have your home address as a waypoint -- at least not filed under something obvious like "HOME". Anyone breaks in and swipes your unit while underwater, they know where you live, know you're going to be away from home for a good few hours and if your house keys are in your car then they have free entry. Even having the dashboard mount on display is a good sign that there is probably one in the car.