gps mounting unit position / compass help??

brownies

Chief Petty Officer
Joined
Jul 5, 2004
Messages
495
I know I'm overthinking this.
Installing another GPS unit and the question came up that it would be better to mount the unit to where it was in unison with the front of the boat. (rather than at an angle in relation to the bow).
For example: If the screen is in the NORTH UP mode, and there is a land POINT directly to the north of the bow, and the boat was MOVING directly toward that point.
The arrow shaped cursor will be pointing directly at the point and you would be leaving a trail on the screen behind it. (it'd look like a "tiny boat on the screen" going north).

NOW......what if the unit itself was turned to face the rear of the boat, YET the boat continued to travel north bow first.....would the cursor "tiny boat" turn around and appear to be backing up?
 

bruceb58

Supreme Mariner
Joined
Mar 5, 2006
Messages
30,454
Re: gps mounting unit position / compass help??

brownies said:
NOW......what if the unit itself was turned to face the rear of the boat, YET the boat continued to travel north bow first.....would the cursor "tiny boat" turn around and appear to be backing up?

No...it wouldn't. The gps is just gathering data location points and puts the indicator on the screen in the orientation that it thinks you are going from the data. The unit itself doesn't care what orientation it is in.
 

Reel Poor

Vice Admiral
Joined
Jan 29, 2005
Messages
5,522
Re: gps mounting unit position / compass help??

Hey brownies.....Been a while.....Did you finish your boat project....It'd be nice to see some pics if you did.

I don't run my GPS in the NORTH UP mode very often. I run it in the HEADING UP mode. The reason for this is all obsticals (that are in your path), channel markers, land masses, ect will always be comming from the top of the screen. In the NORTH UP mode the obsticals will be comming from any direction on the screen depending on which way the boat is heading. For example (in NORTH UP) if your haeding south charted obsticals will be comming from the bottom of the page, west they come from the left and east they come from the right of the page. It can get confusing sometimes, especially running a winding river.

 

brownies

Chief Petty Officer
Joined
Jul 5, 2004
Messages
495
Re: gps mounting unit position / compass help??

I do the same as well (heading up)....Maybe that would have made for a simpler question, but, I just thought "north up" would be easier to make my brain less confused.
I'm fairly certain the "arrow" is dictated by which way the unit "head" is pointed.
Say the back of my boat is stuck on a stump...I run the trolling motor and do a 360. The arrow points up and the screen rotates. (if north stayed up, the arrow would turn as I turned).
So if the screen/unit is dictating which way the arrow is pointing, and I'm pointed upstream and drifing downstream.....Arrow still pointing up yet moving back?

Or, lets make it worse. Save a trail with the unit mounted 45 degrees to my right, facing me....try to re-run that trail in the dark is almost impossible. I understand the compass updating is probably slower than I'm moving, but, I'm just wondering if that 45 degree angle is messing it up "somewhat".

I could check this, but, it's cold out.

That black Bass Boat project "ALMOST DUN"...uhhh...installing GPS units now...could you guess?
I'll post pics in a few days.
 

Reel Poor

Vice Admiral
Joined
Jan 29, 2005
Messages
5,522
Re: gps mounting unit position / compass help??

One thing to keep in mind is that the GPS unit CANNOT determine direction unless it is in motion (faster the better). It can determine where you are but not the direction you facing, hence the screen jumping all around while stationary. In the north up mode the arrow on the display rotates on the screen to show direction of movement, up=north,down=south, right=east, left=west. If your moving forward, backing up, or drifting sideway the arrow will point to that direction of motion. The unit does not know where the front or back of the boat is, it only shows direction of movement. You can mount it facing any direction you want and it will still show accurate direction of movement. In the heads up mode the arrow ALWAYS points to the top of the display and the map display turns to coincide with the direction of motion.

Hope your not confused any worse. :%

Would love to see the pice of the boat. 8)
 

Boatist

Rear Admiral
Joined
Apr 22, 2002
Messages
4,552
Re: gps mounting unit position / compass help??

If your headed to a point to the north in north up mode the arrow will point to the top of your screen.

If your unit is pointed to the bow and the direction the boat is moving if foward the arrow will show your direction.

If you point your unit to the stern the arrow will still point to the top of the unit screen for north but since the unit is now pointed south the arrow will point south even thou your moving north.

The unit assume the unit is in front of you pointed ahead of you if your walking or on the boat it assume the unit is pointed to the bow.
 

bruceb58

Supreme Mariner
Joined
Mar 5, 2006
Messages
30,454
Re: gps mounting unit position / compass help??

The GPS head unit nor the antenna have any directional capability. The only thing that is known is position.

The GPS determines the direction you are going buy collecting multiple position data points and calculating the direction from them.

You can have the GPS unit upside down...right side up...sideways...it will always show the exact same thing on its display.
 

Texasmark

Supreme Mariner
Joined
Dec 20, 2005
Messages
14,544
Re: gps mounting unit position / compass help??

My new little GPS receiver is an Explorist hand held. Trying to get familiar with it.

I used it a couple of days ago to calibrate the compass in the boat. Worked great for that job.......course I had to be moving for it to give me direction info as mentioned.

Obviously much faster and accurate heading info, but I may not always have it with me and the compass is part of the boat.
------------------

While I'm in here, I realize that GPS triangulates your position with at least 3 satellites and that speed and direction are based upon your movements with respect to them; regardless of which direction the unit is pointed.
--------------------

Why then, would you have these functions discussed in this thread? Curious (as usual) as I may get to really like this and later on get a fancy one for permanent mounting in the boat with all the whistles and bells you are talking about.

What references do they use for the display (for the different functions) that must be provided within the instrument since you aren't going to get them from the satellites?

Thanks,

Mark
 

Silvertip

Supreme Mariner
Joined
Sep 22, 2003
Messages
28,758
Re: gps mounting unit position / compass help??

You can set the display mode or "orientation" settings on most GPS unit. My GPS12MAP is generally set so north is always up -- with up being the top of the display. It doesn't matter which way the unit is held -- north is always up. Its the pointer that tells you the actual direction of travel. There are three settings on my unit. "North Up", "Course Up" and "Track Up". These settings have a bearing on how the base map appears. I guess the best way to point this out is that North is North. We can't change that. How a map or your direction of travel appears when superimposed on a map or display can be altered through the magic of computers. The average person tends to hold a paper map so north is up. It doesn't change a thing if you happen to be driving south when reading the map -- the car is still going south which is in the opposite direction of map orientation. You can be sitting backwards in your northbound boat (hopefully someone else is driving) and even though the GPS you are holding is "oriented" south, the sugar trail being left on the screen is headed toward the top of the screen. It's simply all about "orientation" of the display.
 

Texasmark

Supreme Mariner
Joined
Dec 20, 2005
Messages
14,544
Re: gps mounting unit position / compass help??

Thanks Silver, that helps.

Mark
 

brownies

Chief Petty Officer
Joined
Jul 5, 2004
Messages
495
Re: gps mounting unit position / compass help??

I guess my cursor just points the direction I'm moving, regardless off which way the face is pointed. Told ya I was overthinking it....or...just lack of any brain function?
 
Top