Converting Gps marks '66 to Wgs84

[craigathome]

hay all i am looking for some information on converting Gps from Map datum Astrln '66 to Wgs84

from a Garmin 120 to a Garmin 126
can anyone help.

[SatNav]

1. Change the datum in the GPS to WGS84

[craigathome]

that did it thank you.

[Lucky_Phill]

I'll have to dig out my books.

Stay tuned.

Phill

[Lucky_Phill]

OK,, for a fairly accurate conversion:-

AGD66 to WGS84 >>>>>>

- 104 Latitude
+ 067 Longtitude

This is for the Brisbane Long and Lat. There is obviously a small alteration for different areas, and there is even a software program that will do this for you. Ken Fox's Fishing Log. I believe it is advertized in Bush'n'Beach fishing magazine.

Have fun. I did the exact same thing. Garmin 120 to 126. Then when I did that, converted the Marks back into the 120 ( after reseting the Datum to WGS84 ).

Cheers Phill

[SatNav]

1. One has to be very carefull with some of these general block type shifts as a GPS is generally more accurate than the inaccuracy induced into the converted Lat/Long values

[-Henno-]

I recently went to a mark for a wreck just north of the seaway that i hadn't been to in about 4 years when I first bought my Garmin GPS 12. Couldn't find it when my GPS said I was there. Then I noticed it on the sounder a hundred or so metres away.

I also noticed this when fishing Palmy this summer with my old mark for it so I just ended up anchoring with the crowd and using the sounder.

It was suggested by somebody that it maybe the WGS 84 thing but when I checked it was already set to that. Has anything else happened in the last 4 years that could cause marks to wander off?

[SatNav]

1. Nothing has happened in the past 4 years that would cause marks to "wander off" by this amount.

2. There is movement on a yearly basis with coordinates but not enough that you would be able to detect (at this time).

[striker1]

Could it be that the original waypoint was taken when your and my friend Mr Bush had Selective Availability turned on, and now that it is turned off, you are going to a point up to 200 metres off where you first went.

[SatNav]

1. Just remember Mr Bush had nothing to do with turning Selective Availability off

2. Selective Availability induced a general error of 100 metres (or there abouts mostly) but in reality it was generally less then 100 metres. You are lucky Congress didn't get the 500 metres they originally requested and settled for 100 metres.

3. 200 metres error in this country is an immediate indication of using the incorrect datum

[Lucky_Phill]

Pretty well 200. My workings, although not exact, is WGS84 is about 170mtrs SW of the same mark in AGD66, or something similar.

I thought it was Clinton who dropped the SA ? Well, he dropped something, didn't he ?

CHeers Phill

[-Henno-]

This civilian GPS stuff is wearing pretty thin. We had an extra set of digits on navy Seahawks. You could fire up the avionics let the gps lock on while the aircraft was on the flight line, get a mate to shake the hell out of the tail pylon and watch the last 3 digits change. Now that was accurate.

[SatNav]

1. That wasn't civilian GPS but then that's qute a bit over stated as well. Even non augmented military accuracy is not all that much better than straight SPS accuracy these days.

1. Phill would check your 170mtrs SW?

2. Between Noosa and Point Danger and to the precision most recreational GPS can deliver the difference between WGS84 and AGD66 is identical. WGS84 Latitude decreases by 0.095' and Longitude increases east by 0.063'. All up difference is around 204 metres (104m in easting, 175 northing)

3. Difference between a block correction of <0.104> lat, + 0.067 Long to a true conversion is around 20 metres, close to probably twice present day GPS accuracy.

4. Might not sound all that much to some but it's enough to miss a spot completely especially considering the original coordinates could be off by that much again.

[Lucky_Phill]

I will Satnav, the post was just from memory.

Been many a year since I had to do any conversions.

Good info people.

For those that read this and think it may come in handy, try copy and pasteing the thread ' address ' to a word processing program and saving it for later.

Cheers Phill

[SatNav]

If any of you want actual conversion factors from AGD66/84 to WGS84/GDA94 then more than happy to do this. The few seconds it takes to do this correctly outways the myriad of confusing figures that we see these days from many different sources.

Any converison is bsically location specific, well within general geographical areas anyway, so does not require any position that is important but a general location (Lat/Long/Datum).

What's more it's also free, it's official and it will be correct based on data provided.