What's my Heading???

Hi All,
The attached image shows what appears to be a plane I've been looking for for ten years. I took it maybe 3 years ago with a 987; Went back last year with my 1197 to try again and find it-no go;

I intend to use the Lat/Lon in the image which is of course of the boat (41 31.945/070 44.011) not the Cursor position as a search pivot-point to scan around. Had I known when I shot it with the 987 that the Lat/Lon in the image is of the boat not the cursor adjacent to the target I could simply anchor next to it and dive it AFTER getting the Lat/Lon of the Cursor from the unit where they are stored. But at the time I didn't know that.

While I intend to mark with a flag the Lat/Lon of the boats' position and scan around it, I would like to know-can anyone tell me from the image data what the Heading of my boat was when I took this image??

I have tried and tried to figure this out-and maybe it can't be figured out-don't know. In my experience the Bearing data that appears really confuses me-I don't know if the Bearing # indicated is 229 from True North, 229 from the direction/Heading of my boat or something else.

I've moved the cursor while cruising dead north (000) and tried to make sense of the resulting number-readout, by say, moving it at a right angle to the boat (90 degrees) but it doesn't read 90 degrees-hence my confusion as to what it really means.

Any help appreciated-also posted this question to the Yahoo forum and the forum at SideImagingSoft.

Thanks.

I think you will find the lat and long is at the cursor

_________________
John

StrikeBack Tackle
Humminbird Dealer
www.strikebacktackle.com.au

In 2007, as I do a fair amount of searching for things to dive or recover, I called Humminbird right from my boat about this and got straightened out nicely because I couldn't figure out why I was not able to find say, a car I had clearly bagged on side-scan. At that time I would navigate to the Lat/Lon that was on the screen, drop anchor there and dive-wrong move; Whenever I did this I could never find the object.

I now know for a fact that the Lat/Lon on the IMAGE is that of the boat, not the position of the Cursor. I learned that when I mark a target with the Cursor, it creates separate Lat/Lon data of the target. To be clear here, now there are 2 sets of Lat/Lons, one of the boat, one of the target (IF you marked something with the Cursor).

When I go to dive something, first I need to find and log the Lat/Lon of the position of the Cursor because transferring images to my PC does not carry over the position data of the Curosr even tho' I've tried to get it to copy. In the meantime I get the Lat/Lon of the very important Cursor-position in one of two ways:

1) Go to EDIT WPTS; Select the number of the image to dive, and there I will find the Lat/Lon of the target-I write these down;

2) I can also go to the screen that stores all of the images I have captured; Again, I select the one that has the target I want to dive marked with the Cursor and note the Lat/Lon from that window instead-they are the same numbers;

Try this with an image you have that has a cursor marking something on it-compare the Lat/Lon in the IMAGE with the Lat/Lon of the CURSOR using either of these methods-they will not match, and this solved my problem.

Now I know how to get the position data of where the Cursor is. When I dive now I can also just hit GO TO and naviagte right to the cursor position and drop anchor. This works so well at least 70% of the time when I dive it I land right on the deck of the vessel, or roof of the car etc.. At most I'm off by maybe 20 feet due to currents or wind shifting my boat a bit while the anchor descends.

I still don't know what to do re: my original question re: Bearing.

Hope it helps.

neddiver,

You are correct that the coordinates in the snapshot are of the boats position. It would be nice to have the coordinates of the cursor as well posted at the top. Maybe a wish list item! When you hit the mark button, the waypoint created is at the position of the cursor, not of the boat.

So, by pressing MARK and taking this snapshot, you have already marked this target with a waypoint. Also, if you have not changed the file name of the snapshot, this will be your waypoint name! Very Happy

The bearing 229 is from True or Magnetic North (which ever you have set to use).

To calculate the Heading you will need to do a little algebra.

You are going to need to find the angle of the triangle created from the boat, to the cursor, and back to the center line. We have three numbers to work with. The Distance to Target of 78ft, Cursor from Center Line of 84.1ft, the Depth of 54.1ft and the Bearing of the Target at 229.

The first thing we are going to need to do is accurately calculate the targets distance from the center line. The number of 84.1ft is actually the Slant Range to target and not the Horizontal Range. Since we are talking right angles at the base, we can use the Pythagorean Theorem to work out the length of the missing side.

We would need to solve for b. So the equation would be:
b2 = c2 - a2 (c = slant range 84.1 , a = depth 54.3)
b2 = 7072.81 - 2948.49
b2 = 4124.32
b = 64.22 ft

Assuming you were travelling in a straight line, we now know two sides of another right triangle. WE have the Horizontal Distance to target from the Center Line of 64.22ft and the Distance to Target from the Boat of 78ft. With that, we can calculate the angle of the top angle of the triangle. Then we can add it to the given bearing to give us the reverse bearing of our direction, then subtract 180 to find out heading.

To do this, we will need to use Sine, Cosine, Tangent.
Sine = Opposite/Hypotenuse
Cosine = Adjacent/Hypotenuse
Tangent = Opposite/Adjacent

Since we know the side we need to use are the Hypotenuse and the Adjacent, we can use the Sine formula to find our angle.

Sine(A) = Opp/Hypot
Sine(A) = 64.22/78
Sine(A) = 0.823
A=Sine-1(0.823)
A = 55.4

So now, we know our bearing of 229 and we know our angle to target is 55.4, we can add these together to get 284.4. This is bearing is to the rear of us pointing to where we came from, so this is the exact opposite of our heading. So we would subtract 180 to get our current Heading of 104.4.

Hope that all makes sense! Good Luck!

Robert Gecy

_________________

"SideImagingSoft.com - Humminbird Side Imaging Forums"

Wow that was great-thanks; I wouldn't ask if it wasn't important. These sites are terrific. I will let you know if I find it.
NEDiver