hey just sedning a post so i can send a a pm...lol. sorry guys
love ya's
me ooxx
hey just sedning a post so i can send a a pm...lol. sorry guys
love ya's
me ooxx
Phil, Relative to 27°S 153°E (Brisbane there abouts) the difference between AGD and WGS84/GDA94 is 213.3 metres (+/- 0.050m).Originally Posted by Lucky_Phill
With respect those numbers the difference AGD to WGS/GDA in decimal minutes is 0.095' less in latitude and 0.054' increase in longitude..... AGD to WGS minus 104 Lat and add 067 Long ( notice the 3 numbers ) ?
That makes 27° 00.000'S 153° 00.000'E AGD becomes 26° 59.905'S 153° 00.064'E in WGS84/GDA94
Cheers, Kerry.
That much?? that surprises me. Sounds like it must be from what you and phil said. As an example, recently I picked up the wreck on the beach that is south of tangers, and after puting it into my gps (in correct AGD) and seting the gps back to WGS, I plugged the WGS spot into my AGD map to see what the difference was, and it did not look to be that much.
Anyway, even though I always convert to the right format to suit, at least now I know what the exact variations are.
Apart from that, the rest of the advise I gave sharkbait was right,,, wasn't it? At least in simple terms.
So what do I do when I am given a mark like 23.41.769 - 151.38.525 and my GPS only takes xx.xx.xx - xxx.xx.xx
The last set of numbers have one more than I can fit in, and of the last set of numbers the first digit only goes up to 5 on the GPS. Is it something to do with the GPS I have. It is one of the old Magellan Pioneers'. I have looked throught the menu on it and changed things around and tried it, but honestly, I have no idea what I am doing.
Any help would be appreciated,
Corry
Corry, It sounds like your sounder is expecting Degrees, Minutes & Seconds rather than Degrees, Minutes & Decimal Minutes. That would explain why it only goes up to 5 (i.e. 60 seconds in a minute, so it would go to 59 and then back to 00)
I am not sure how to convert between the two but at a guess it would be simply a case on multipling the decimal minutes by 60 to convert to seconds e.g.
.750 decminal minutes = 45 seconds (.750 x 60 = 45)
In your example of a mark of 23.41.769 - 151.38.525, I think the correct mark would be 23.41.46 - 151.38.31. Someone else might be able to confirm if this is the right way to convert - over to Kerry.
Cheers,
Mark
The Pioneer can be configured to accept dDD° MM.mm' (DEGMIN) dDD° MM' SS" (DEGMINSEC) and UTM.
Limited to whole seconds in DEGMINSEC or 2 decimal minutes in DEGMIN.
23.41.769 - 151.38.525 would appear to be 23° 41.769' - 151° 38.525' based on the latitide decimal minutes being greater than 59.
Your receiver appears to be currently configured to DEGMINSEC (limited by only accepting 59 seconds). Not a very good format to use at all, so forget any thoughts of conversion.
In the Pioneer Press [MENU} until SETUP is displayed and press [ENTER]. Press [ENTER] again and you should see the coordinate system flashing. Use the RIGHT/LEFT arrow's to scroll the coordinate systems and press [ENTER] when DEGMIN is displayed.
Enter those particular coordinates by rounding as 23° 41.77' - 151° 38.53'
Can highly recommend reading the manual [smiley=2thumbsup.gif]....and changed things around and tried it, but honestly, I have no idea what I am doing.
Cheers, Kerry.
It's been a good thread this one. It got me thing about some marks i have got of the internet and out of books.
Marks such as 32.58.36S 151.45.09E
I have been entering them as ddd.mm.mm and just add zeros to the end of them
When i go to these spots there is nothing there.
Just looking at me etrex
Could it be that i should enter them as ddd.mm'ss.s? and then i might find them ?
Hmmmm might have a play with this thing.
Kerry out of interest, how far out would my marks be if this was the case and i was in sydney (roughly)?
Based on mistaking 32° 58.36'S 151° 45.09'E for 32° 58' 36"S 151° 45' 09"E would be around 450 metres.
As for datum difference around Sydney then based on 33S 152E about 216 metres.
Really all published or internet marks should be treated as suspect as there's generally no guarantee as to the certainity of the format or the datum.
The "unknown" is what some publishers call a "fudge factor", when really it's "trash for cash"
Cheers, Kerry.
Coordinates are normally expressed in hours – minutes – seconds
27044’13 is obviously 27 hours 44 minutes 13 seconds. As one hour equals sixty minutes then this “one hour” can also be called “one degree” - makes it easier!
Your GPS SETUP MENU x NAVIGATION will omit the main “degree” figure and simply show MM.MMM’. It does this because the primary degree figure (27) cannot be altered to anything else whereas the “seconds” can. The MMM is simply 1/1000ths of the MINUTE. So, in the GPS setup, you scratch about till you find the MM.MMM’ setting and select it (it is usually the default one anyway!) …. And remember that this principle applies to BOTH Latitude and Longitude. Now, the above coordinate will look like this:
27044’135
If you had a hot spot to locate with a coordinate of say:
27037’272 you would not be able to insert it all (the 2 bit) into the GPS if you had the SETUP as in the first example above (not enough digits!!)
However the latter example with its 7 available digits would accept the coordinates quite happily and be more marginally more accurate.
The difference is not quite as huge as you would imagine but it is necessary if you are looking for a very isolated peak and need to be as close as possible! It can also be seen by the red lines on the sample chart above that it is now simple to plot in the “.272” bit and vice versa from the chart (or your mate) to your GPS.
1 degree of Latitude = 60 nautical miles so S270 to S280 = 60 nautical miles
1 Nautical Mile = 1832 metres
1/10th. Nautical Mile = 183 metres
1/100th. (MM) = 18.3 metres
1/1000th. (MMM) = 1.83 metres
So in summary, the difference in putting the 2 (.002) into your GPS makes a difference of about 2 metres!
Also important to check your GPS is set up to WGS84 being the last decent update from hydrographic surveys in Qld, i.e. your latest chart is already 20 years old!
As even the best of GPS’s still contain errors of up to 50 metres +/-, the offending “third digit” is not all that critical. If you can only see “two digits” in your last grouping of coordinates, go to the SETUP menu and look for the MM.MMM one.
By the way, Longitude is a different ball game altogether and although we can guesstimate on it sometimes, it follows totally different rules than the 1 nm = 60 minutes! In our latitude however, it can be (almost) said that 1 nm of Longitude also just about equals 1 nml – but not exactly! About 70% of the cost of a GPS unit is supposadly in the antenna so without a good one and as high possible with no obstructions about it, the better it is!
Thanks everyone for answering my queries
what a wealth of knowledge to be able to tap into
Thanks, Again
Kris
Sorry not obvious (to me). If it was obviously Degree Minutes and Seconds then why not actually make it Degrees Minutes and Seconds?.... Coordinates are normally expressed in hours – minutes – seconds 27°44’13 is obviously 27 hours 44 minutes 13 seconds.
27°44’13 is ambiguous 27°44’13" is not and clearly intended to be DMS.
Sorry but this is rather confusing. First mentions that 27°44’13 is obviously Degrees Minutes and Seconds"? Debatable, and then goes on to setting MM.MMM' (1/1000ths of a MINUTE) and now the above coordinate looks like 27°44’135 ? well if 27°44’13 is Degrees Minutes and Seconds? then configuring to MM.MMM' the above "same" coordinate should look like this 27°44.217' otherwise following on that 27°44’13 is Degrees Minutes and Seconds then 27°44’135 should rightly be taken to be 27°44’ 13.5" (in the same context).
But really it is quite simple to mistake as these days there are very few GPS receivers that don't have Degrees Minutes and Seconds format as dDD° MM' SS.s" (to 1/10 of a second) so 27°37’272 could be input/accepted as 27°37.272' (DM.m)or 27°37’ 27.2" (DMS) without a problem. For sure with some older receivers and specifically some particular makes there were some limited to whole seconds but in today's environment whole seconds is an antique limitation..... If you had a hot spot to locate with a coordinate of say: 27°37’272 you would not be able to insert it all (the 2 bit) into the GPS if you had the SETUP as in the first example above (not enough digits!!)....
Many GPS receivers also have a decimal degrees format such as dDD.ddddd° (5 decimal degrees) so what's stopping someone from entering 27°37’272 as 27.37272° ?? has been known to happen. So the available digits doesn't really reflect the format.
Although it's probably better for users to think it could be 50 metres +/- than believe the claims of sub-metre or even worse accuracy within a "few feet" 50 metres is probably not the norm these days..... As even the best of GPS’s still contain errors of up to 50 metres +/-, the offending “third digit” is not all that critical.
The system specifications are 13 metres (SIS) 95% of the time world average with worst case scenario (down to 22 satellites) at 36 metres 95% of the time. The system specifications are based on a 24 satellites constellation and currently there are 28 on-line.
Most recreational receivers probably fit into the less than 7 metres some of the time, less than 10 metres the majority of the time and less than 15-20 metres most of the time but not all of the time as there's the other 5% of the time where accuracy "can be" bad, sometimes real bad, at times even tens of kilometres. It's this "other" 5% that one doesn't want to want to occur when say running the beacons in the dark solely on GPS.
So in affect users who simply drop the last digit for decimal minute inputs "could" introduce a position error several times greater than generally available accuracy. Even rounding 3 decimal minutes to 2 decimal minutes has the possibility of around 13 metres, which is equal to the system's accuracy specifications.
Cheers, Kerry.
PS that 1nm=1832 metres should be 1852 metres.
If they weren't confused with my explanation Kerry, they sure as shit are now after viewing yours! Good pick up on the typo in 1832 though! My sloppiness must cease immediately!
Well sometimes one thinks long and hard as to if trying to spell things out as they are will confuse further or not confuse.
But generally what the hell, can only tell it how it is and if anybody wants to dispute that then lets do that.
Cheers, Kerry.
OK - my GPS has an 'accuracy' meter (for want of a better way to describe it) which when I am on moreton bay usually reads about 4 - 15m.
Is this accurate? Say, given that my GPS is programmed for Brisbane's time zone - and accuracy is at 10m, does that mean I am within 10m of the co-ordinates currently being displayed?
And in the other scenario - If I punch in a mark that I want to go to (and given datum etc are the same) does that mean when I come up on the mark, I am within 10m of the co-ordinates I punched in, or is it 10m plus the 50+/- that kerry mentions?
Cheers, Kris
use your gps to get you somewhere near the mark and then use your sounder, you may find a better spot
cheers
blaze
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