GPS chart settings : Electronics

balou · Posted: Sat Jul 14, 2012 9:57 pm Post subject: GPS chart settings

Took the new tub for a run to cape hotham this morning. Boat handle like a dream but I have concerns about my new HDS 10.
I had a Garminh 298 in the old boat and transferred the marks to the new HDS 10. Painful but easy enough.
I entered 10 marks for hotham and everyone of them was about 200m + differrence between the Garmin and Lowrance.
Some of my marks I couldnt even find anything and all of these are my honey holes.
One of th marks ended up on a dry reef itself.
I was p...ed and spent most of the day sounding.

I thinking of getting a HH garmin GPS and hopefully get all my honey holes into the Lowrance that way.
Hopefully the 2 garmin GPS will be within 5-10m.

Any other ideas as I stressing at the moment. I have accumalated these mark over the last 10 years and not keen to start from scratch.

Only manage a 6-7 meter long queenies for the day.

Trier · Posted: Sat Jul 14, 2012 10:10 pm Post subject: Re: GPS chart settings

Hi Balou, silly question perhaps, but are the map datums the same on each unit?

Sad day fishing when you can only manage a half dozen big queenies.

Lats · Posted: Sat Jul 14, 2012 10:31 pm Post subject: Re: GPS chart settings

I have a Garman, maybe you can give me your marks and we can go out together and I can put you back on track :wink:

But really, that would suck

Lats · Posted: Sat Jul 14, 2012 10:49 pm Post subject: Re: GPS chart settings

Got this info from http://www.oziexplorer3.com/support/ozi ... atums.html. Hope it helps

The GPS Upload/Download Datum - must always be set to match the datum your GPS expects its position data to be transmitted in.

For Garmins this Datum should always be set to WGS 84.
For Magellans this Datum should always be set to WGS 84.
For Lowrance/Eagle - Most should have this Datum set to WGS 84 but care should be taken if using a GlobalNav 200 or Eagle Explorer as certainly some of these units require the Upload/Download Datum to be set to the same datum as the GPS is set to.
The GPS NMEA Output Datum - must always be set to the same datum that the GPS uses for the positions it sends in the NMEA sentences.

For Garmins the Datum must be set to the same as the Datum setting in the GPS. If using moving map mode and you change the GPS datum then you should always change this datum also.
For Magellans you need to check this, some models output in WGS84 and others such as the 315/320 output in the Datum the GPS is set to.
For Lowrance/Eagle - Most should have this Datum set to WGS 84 but care should be taken if using a GlobalNav 200 or Eagle Explorer as certainly some of these units require the NMEA Output Datum to be set to the same datum as the GPS is set to.

balou · Posted: Sat Jul 14, 2012 10:54 pm Post subject: Re: GPS chart settings

Just google my old garmin sounder and it uses Wgs-84 datum while Lowarance uses WGRS-84. (default)

Wonder if this R has any thing to do with accuracy....

balou · Posted: Sat Jul 14, 2012 10:57 pm Post subject: Re: GPS chart settings

Oopes thanks Lats just saw your post...

12 hours on the water and trying to read info is a challenge in itself... :bonk:

cuddlescooper · Posted: Sat Jul 14, 2012 11:15 pm Post subject: Re: GPS chart settings

check that the gps is set in 'degrees and minutes' or degrees, minutes and seconds. they need to be the same on both GPS's.

balou · Posted: Sat Jul 14, 2012 11:38 pm Post subject: Re: GPS chart settings

Cuddles, I wish it's was that easy. I dont have contact with the dude which purchase my old boat.

I've just read the Garmin 298 manual and it's in deg/min /sec same as the lowrance.

It was also taking about Garmin using a loranTD system.. Not sure what that's all about but fairly confusing

passenger279 · Posted: Sun Jul 15, 2012 12:06 am Post subject: Re: GPS chart settings

I had the same problem borrowing a mates marks out here, they all seemed to be a hundred meters or so off. That was going from a Garmin to a Lowrance. Let us know what you work out.

Jeremy

Lats · Posted: Sun Jul 15, 2012 12:08 am Post subject: Re: GPS chart settings

balou wrote:

Cuddles, I wish it's was that easy. I dont have contact with the dude which purchase my old boat.

I've just read the Garmin 298 manual and it's in deg/min /sec same as the lowrance.

It was also taking about Garmin using a loranTD system.. Not sure what that's all about but fairly confusing

Not saying that this is fool proof but if your marks on your new GPS are in degrees/minutes then try changing it to add the seconds. Before you do it, copy a mark down and see if it changes once you add the seconds part. The rounding up or down might be your missing metres.

But if your marks in your new GPS already have the seconds added, then disregard what I have just said.

Failing that, I would ring Lowrance

Trier · Posted: Sun Jul 15, 2012 12:31 am Post subject: Re: GPS chart settings

From http://khuts.org/index.php?option=com_c ... &Itemid=85
Along the line Lats is thinking, maybe this could also be a cause...

Lat/Long

For some reason, most GPS receivers have the default setting for reporting the position in latitude and longitude. This being the standard ‘navigating’ format, it satisfies the majority of users that they are now truly ‘navigating’, even if they don’t fully understand the system.

Within the lat/long notation there is a further divide: while traditionally one used degrees, minutes and seconds of arc to describe a position, modern usage also allows decimal degrees, and degrees and decimal minutes :

degrees, minutes & seconds of arc S 35° 55’47.1”, E 148°28’42.1”

decimal degrees S 35.92976°, E 148.47835°

degrees & decimal minutes S 35° 55.786’, E 148° 28.701’

All of the above positions describe the same spot - Four Mile Hut, SE of Mt Selwyn in NSW.

Quite apart from the possible confusion caused by different formatting, lat/long positions are very hard to transcribe to a topographic map because the grid shown is of a totally different system, and because of the difficult mathematics involved in minutes and seconds of arc.

ronje · Posted: Sun Jul 15, 2012 1:01 am Post subject: Re: GPS chart settings

Hello Lats

It could be as simple as the 2 GPS units using different datum mapping.

They all come with the different datums installed in the unit's menu. When installing the unit, the menu gives u options. One of those options is for u to tell the unit which map datum to use.

The standard datum is WGS 84. If you don't choose an option it will have a defaults one (usually that's WGS 84). If however, you choose something else not knowing what the hell the GPS is asking you, you can easily end up with different positions on the map.

You already have the data. There's obviously a difference.

First step is to find out what datum the points were set up with.

I could lead you through a convoluted sequence of working out which datum was used for your original GPS. Can be bl..dy painful and frustrating though.

Or you could send me a google earth image using an "X" marks marks the spot of one of the points on yr HDS10. It can be any point anywhere just as long you can recognise it on a map. Use reasonable zoom so u can get to within 5 metres or so. Ignore what google says the lat and long is.

Then also give the lat and long reading contained in your GPS for that very spot.

My email a/d is ronje1@optusnet.com.au

The one big thing you have to your advantage is that you can go to one of your honey holes and position your boat right on it.

Do that.

Then look at the GPS. Write down the lat/long info displayed.

Go to the options menu

Follow this sequence.

Lats · Posted: Sun Jul 15, 2012 5:16 am Post subject: Re: GPS chart settings

Thanks Ronje but my GPS is good to go. Balou is having the problem :mrgreen:

ronje · Posted: Sun Jul 15, 2012 7:35 am Post subject: Re: GPS chart settings

Sorry Lats.

Senior's moment there!

Offer stands though.

balou · Posted: Sun Jul 15, 2012 2:20 pm Post subject: Re: GPS chart settings

Thanks for the offer Ronje.

If I have the cordinates from old sounder and cordinates from the new sounder at exactly the same location.
Is it possible to work out what the old sounder datum setting was?
If I get a garmin Hand held GPS and set it up with the datum setting as the old unit I'm back in business.

I rarely use FFF marks but I punched in the fenton co-ordinate afew years back on the old GPS and could not find any of the wrecks out there.
At the time I didnt think to much about it but now I'm certain the old gps was on a different datum setting.

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