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snappa
09-06-2003, 01:47 PM
hi all
i am chasing the wreck "neilston" i think thats the spelling. ???
does anyone know and could you give me the gps marks
for the wreck.
a trip out if you can remember.
snappa

Lucky_Phill
09-06-2003, 01:51 PM
153.20.020 27.11.147 NILSON capt nilson (WGS 84 )

snappa
09-06-2003, 02:25 PM
lucky phil
thanks for the gps marks for the nilson
what is wgs 84 mean
many thanks again
by the way have you any wrecks on the outside of moreton
i heard that there is plently of trawler wrecks and one i am keen on to find is about 12 ks east of cape moreton
snappa

Kerry
09-06-2003, 05:51 PM
lucky phil

thanks for the gps marks for the nilson
what is wgs 84 mean


Well I find that rather a worry :-X asking for "GPS marks" and not knowing what WGS84 means :o.

Cheers, Kerry.

Big_Kev
09-06-2003, 07:08 PM
LOL
Yeah thats a good one Kerry.
Cheers Kev.

grey_inflatable
10-06-2003, 05:30 AM
ha mate why u want to know wrecks for.
is it for diving or fishing,if it is diving there many in the bay sounds cool
c u

xxxxhornet
10-06-2003, 12:22 PM
G'day Snappa - mate I had to look in my manual - it means World Geodetic System 1984.

Got me stuffed either what importance it has though so that makes two of us.........
I believe its to do with what part of the world you are operating the gps in.

cheers

Kerry
10-06-2003, 03:34 PM
G'day Snappa - mate I had to look in my manual - it means World Geodetic System 1984.

Got me stuffed either what importance it has though so that makes two of us.........
I believe its to do with what part of the world you are operating the gps in.

NO it's really got all to do with finding what you are actually expecting to be looking for. The same part of the world can have several different datums, just like we have in Australia along with the confusion that they cause.

Basically the same coordinates used with the wrong datum (and WGS84 & GDA94 & AGD66 & AGD84 & WGS72 etc are all datums) will be a DIFFERENT physical point on the ground. The difference between AGD and WGS84 is around the 200 metre mark.

Cheers, Kerry.

webby
10-06-2003, 03:52 PM
It amazes me that people using gps systems, dont know what datum they have setup in their gps's.
Would hate to be following them on a night jointy if their using their gps for navigational purposes.
It would be like missing the beacon by 400m and finding yourself high and dry on some rocky outcrop.
regards

sharkbait
10-06-2003, 04:24 PM
Not everyone knows everything like some of you seem to think you do, why don't you just explain what it means. Its more than likely their gps is set to wgs 84 anyway.

banshee
10-06-2003, 05:04 PM
Okay,something that Ive thought about but never found the answer to,if I enter a mark from AGD84(example) into my unit while it is in this datum,then change back to WGS84 does the mark transfer accurately?Likewise if I change format,enter a mark then change back to the format I prefer to use, does this mark I have just entered also transfer over accurately?

SteveCan
10-06-2003, 06:10 PM
Hi Banshee -

No - when you change the datum - the numbers of a waypoint will not convert over, they stay exactly as you entered them. the only difference is that as Kerry said earlier, those co-ordiantes will refer to a spot on the ground somewhere else :P

WGS84 is very much the standard - Kerry could give you the technical expanation why I guess, and my GPS came with that set as default. I have never had reason to change from WGS84 as all of the points I have are in the same format. When giving or receiving GPS marks to anyone the Datum should be specified or those points cannot be trusted...

Cheers
Steve.

peterbo3
10-06-2003, 06:42 PM
Evening Banshee,
I may be wrong but I believe that modern Charts using a Datum other than WGS 84 will have a correction for Lat & Long (in Notes at the bottom of the Chart)to enable co-ords plotted on these charts to be adjusted so that a true WGS 84 location can be accurately plotted on them. This adjustment is similar to Magnetic Variation but applies to a position as opposed to a compass bearing. Conversely, a position on an old chart should be able to be converted to WGS 84 & hence an accurate GPS fix obtained in real time whilst at sea..

Kerry
11-06-2003, 04:32 AM
.... Its more than likely their gps is set to wgs 84 anyway.

Is it now ??? but shouldn't users know what their unit is set to instead of making assumptions.

"Explain it", I can try. The following is a simplistic view of why there is a difference and the link outlines what it can mean in the real world. Any questions, feel free

http://www.cqnet.com.au/~user/aitken/gps/datum_diff1.jpg

http://www.cqnet.com.au/~user/aitken/gps/datum.htm

Cheers, Kerry.

Kerry
11-06-2003, 04:46 AM
Okay,something that Ive thought about but never found the answer to,if I enter a mark from AGD84(example) into my unit while it is in this datum,then change back to WGS84 does the mark transfer accurately?

Most GPS receivers do BUT there's some that don't (didn't) and the best way to check (without knowing the make/model of your GPS) is to actually try it. "Some" very popular units in the early days DID NOT and is another possible reason why many of the marks kicking around today are rather suspect.

The change won't appear to be much in Lat/Long but the change will be enough to notice.


Likewise if I change format,enter a mark then change back to the format I prefer to use, does this mark I have just entered also transfer over accurately?

Haven't seen a unit that won't do this with regards formats.

However the biggest problem with formats is the umteen ratty ways that many are published/printed these days. Indiscrimate use of decimal points and the total lack of identifiers can contribute to bigger errors than even exists with datums. So simple to eliminate format issues and fail to see why publishers can't do it right in the place.

http://www.cqnet.com.au/~user/aitken/gps/format.htm

Cheers, Kerry.

Dino
11-06-2003, 08:39 AM
If you are such an expert with your equipment, you shouldn't have a need to to follow him!

xxxxhornet
11-06-2003, 01:19 PM
guys, guys, guys,

Somebody has to say this......

Rather than puffing our chests out about what bigtime gps users we all are, how about helping us lesser folk who are learning the ropes....isnt that what this whole site is intended for.

I believe a simple question was asked about 6 or 7 posts ago.......

cheers - just my 2 cents worth.

Lucky_Phill
11-06-2003, 02:55 PM
Ok, since I started with the reply, I'll help out.

In your Settings page ( sometimes they are called navigation ) in your GPS you will find all sorts of " Datum ". Please ensure that this is set to WGS84 as you will find this matches the " Datum " on most Navigation Charts from Sunmap etc.

You will find the " Datum " in the Legend area of the chart.

The difference between AGD and WGS Datum is 170 meters South West. There is a formula for working this out, but I won;t go into it here.

Let's just say, make sure your GPS is in WGS84 Datum and that anyone who gives you a GPS mark tells you what Datum is being used.

Datum is probably a fancy word for Data or Information that describes the lines and squiggley things on the chart. :o

This Datum thing has been a problem for quite some time now. My advice to anyone buying a GPS is to READ the instruction manual, from start to finish. If still in doubt, post the question here.

Another thing to remember, is that some GPS's , particuarly the hand held jobs only go to 2 numbers in the seconds as opposed to Hard wired units. Therefore < and it is only my opinion, that Hand Helds are not as accurate as hard wired units. How can they be ?

For more info on calculating Datum, GPS points, long and lats from charts etc, please send me next weeks Lotto numbers and I will fill you in.

;) ;D ??? :P ::) ;)


Phill

peterbo3
11-06-2003, 03:33 PM
Phill,
I will get those Sat night lotto numbers over to you first up Sun morning. ;) ;) ;)

Lucky_Phill
11-06-2003, 04:34 PM
I need them by Friday arvo Peter ;) ;D

Kerry
11-06-2003, 04:47 PM
.... The difference between AGD and WGS #Datum is 170 meters South West. #There is a formula for working this out, but I won;t go into it here.

Phill, probably needs some clarification as the difference between AGD and WGS is approx 200 metres North East. AGD to WGS effectively reduces the Latitude and increases the Longitude.

Example (for anybody who wants to check their GPS)

35 00.000'S 150 00.000'E AGD66
is
34 59.906'S 150 00.071'E WGS84 (GDA94)

However (and not wanting to confuse things that are already confused) if one was to use "AGD coordinates" and input them into a GPS "set to WGS84" then the coordinates have not changed but the point on the ground has "physically" shifted South West, but this type of scenario is a little different when one is referring to the difference between AGD and WGS, which is technically North-east.


Another thing to remember, is that some GPS's , particuarly the hand held jobs only go to 2 numbers in the seconds as opposed to Hard wired units. #Therefore < and it is only my opinion, that Hand Helds are not as accurate as hard wired units. #How can they be ?

Accuracy and Precision are 2 different things and there's certainly nothing in the thinking that hand held accuracy is any way different to any other style of GPS.

Not too many handhelds around these days that don't have the same precision capabilities as any other fixed model. Actually when handhelds were restricted in the output so were many other models. Had a lot to do with manufacturers thinking, GPS accuracy specs at the time in the days of selective availability.

When the system was only capable of less than a hundred metres it was a bit deceptive showing accuracy to a foot, meant bugga all but give users more decimal places and they'll swear it's as accurate as the display shows, which is a misconception.

Cheers, Kerry.

Kerry
12-06-2003, 08:40 AM
On the subject of "Handheld GPS accuracy" a little comparison between 2 GPS receivers in May 2003.

http://www.cqnet.com.au/~user/aitken/gps/3133gps2w.jpg

- Data recorded concurrently side by side over 24 hours
- both using the Standard Positioning Service mode
- 95% accuracy is 4.3m & 4.8m
- one is a superceded handheld
- one cost $500, the other is $25,000+

The contrast is what it's all about and that contrast is which one is 0.5 metres "more accurate" than the other and which one is worth $24,500+ more than the other.

Cheers, Kerry.

Lucky_Phill
12-06-2003, 12:18 PM
That's all very well, but have you ever tried to back track on the Track Log on a hand held.

The pixel count is poor compared to the Hard wired units. This is what I'm trying to get across.

Pixel count and screen size comparing HH and HW is not contest.

Phill ;)

CHRIS_aka_GWH
12-06-2003, 01:24 PM
if only we could rate topics like we can photos now - THIS ONES AN 8.5 - entertaining, informative, bit of biffo - good stuff.

I'm actually intrigued that some guys seem not to have read their owners manuals, most of this is in there - at least my Lowrance has it. I often sit down with a beer, get out my motor, GPS & sounder manuals & reread them. I'd do it twice a month & I still come across stuff I didn't know. :-/

chris

spike2
12-06-2003, 02:26 PM
whats a G.P.S ;D

Lucky_Phill
12-06-2003, 03:12 PM
G.P.S stands for:-

Geothermalnytricladone Pyroflamolightoboomo Systiometricoboringo

I think ?

jaybee
12-06-2003, 03:15 PM
can you pronounce them as well as u spell em phil ;D

Lucky_Phill
12-06-2003, 03:29 PM
OK Chris, #here's more.


Latitude : # 1 degree = 60 minutes
# # # # # # # # 1 minute = #1852 meters or 1 nautical mile
# # # # # # # # 0.1 of a minute = 185 meters

and the Longitude minute = 1640 meters ( mostly ), #because of the Earths curviture, it would be 1654 meters at Brisbanes Longitude.

Going back to 0.1 of a minute = 185 meters

153.24.100 is the same as 153.24.10 as per Hand held, ie:- 185 meters past 153.24.000. # #Now, 153.24.155 on a Hard wired is 286.75 meters past 153.24.00, but the hand held will tell you # ( as it will read 153.24.15 ) it is 277.5 meters past 153.24.000

This may be only 10 meters difference, and in the scheme of things not important, but sounding in water less than 20 meters with a 10 degree transducer means you miss the object, ledge, reef, wreck etc alltogether. # #10 meters either side of a channel, is.........bottom.

And onto the next one............nuffin like a good debate, if that's what this !

Converting AGD to WGS.

Decrease Latitude by 095 and increase Longitude by 058, which equates to pretty close to 170 meters. #Now, having said that, The Department of Transport Navigation Charyts say:- #decrease Latitude by 5.8" and increase Longitude by 3.9", whatever that means ? # Just thought I'd put that one in for no apparent reason, but it is true.....................


The thing is, as I have said, Initialize your unit to WGS and at sealevel, get all your marks in WGS, read your manual, have a beer, and if you need confusing, please post your request here... ??? # # # # #::) # # # ;D # # # #:o # # 8) #;) #;)

Phill

Big_Muddie
12-06-2003, 04:03 PM
Most interesting. I checked my handheld - Lowrance GlobalNav 12 - purchased April 2000. Precision is to 3 decimal places.

Kerry
12-06-2003, 04:29 PM
Phil, well what is #??? so called accuracy issues between 2 digit (out of date) handhelds v so called hardwired (that also were no different in their day) or pixel count and screen size, they ain't even close to the same, make up your mind.

No 10 metres is not important and if anybody thinks it really is then they are using their equipment without fully understanding the operation and limitations of the equipment.

Actually it's a lot more than 10 metres with some of those now old (and basically obsolete) receivers BOTH Handheld, fixed mount or any mount.

But if 10 metres isn't important then 216 odd metres (which is what the difference actually is around Brisbane) isn't even close to 170, where does this BS come from #:o.

The one thing that really makes sense is "read the manual" #[smiley=2thumbsup.gif], it's amazing how many have this "appliance" approach and never bother reading the manual. Like Chris this also intrigues me.

Maybe the question to some should be "What's so scary about the manual", it's really quite interesting #;D


Cheers, Kerry.
#

Big_Kev
12-06-2003, 06:06 PM
What's so scary about the manual
Kerry The Old Man Of Sea says "Typical Aussie male waits for things to turn to shit before he reads the instructions"
At least in my case this seems to be true.LOL
Cheers Kev.

jaybee
12-06-2003, 06:14 PM
yeh i agree with kev, instructions (manuals) usually turn into destructions, by the time most of us read em :-X
cheers

Lucky_Phill
13-06-2003, 09:41 AM
The 170 meters was given to me in a offshore navigation course. ?

The old Hand Helds had 2 digits, OK, so the newbies have three. ?

What was the original question ?

Still, even if I was given a Hand held for " water " work, I would trade it asap, wouldn't even bother to use it. Just my personal opinion. ?

I admire your involvement in these posts Kerry, and agree with you 99.9% of the time. I suppose this one boil;s down to a slight difference of opinion and being set in one's ways.

For the record, my GPS is accurate as I need and have never failed to find a reef, wreck, shopping trolley or Lazy Grinner hanging on the bottom.

BY the way...........OH that's right NSW won. &^%%$##%$%&^&**(()()(&%$##@$ mongrels, we'll get ya's next time ;D ;D ;D

Kerry
13-06-2003, 10:32 AM
Phil,

For sure one can't get in the way of personal opinion, it's one of those things. With all the GPS gear on the boat I still prefer using a 1991 model, still as good as the rest and has BIG numbers and that's very usefull these days ;). Agree handhelds aren't for everybody or every application as it does come down to one's own personal requirements with exactly what they want to do with the thing and where.

It's like the "Which GPS should I buy" question, can't/don't/won't give an answer, I'm not the one using it and don't know the total situation. Some silly questions could be, How blind are you, how big are your fingers .... but enough of that.

The unfortuneate thing is that many of the myths somehow get turned into "facts" and as you probably am aware there's really quite a few of these already kicking around out there.

Do you actually still have a model with a 2 digit "restriction" (in today's world). It sounds like one of the "M" models, if so there has been some software upgrades (for some models) that will fix things.

As for the 170 metres that one beats me (which navigation course ;D), there's no where in Oz that gets that low. Off the top of my head the smallest shift is around the SW cnr of WA at about 190 metres?

Cheers, Kerry.

MangroveJase
13-06-2003, 02:11 PM
Is there a prize for this competition? ;D :-X