Calculating Compass Headings?

[Dubious]

Greetings,

My wife and I were at a small dive park last night which had a map of where each attraction/wreck was located. They have headings to each of the attractions/wrecks from the dock. What I want to know is if there is a way for me to calculate the heading from attraction/wreck to another attraction/wreck based off the headings from the dock? It would be nice to create a course without having to surface to grab heading from the surface buoy markers. I feel like this would be easy if I had a map that was to scale, but that is not the case.

Thanks for your input.

Dubious

 

[Justin Bove]

You just need a compass and ruler. What you are looking to do is create numbered waypoints and then headings from each waypoint on your journey.

 

[tursiops]

Two ways I can think of:
1. Use trigonometry and a calculator.
2. Redraw the map to scale using the info on it, and measure any angles/distances you want from your drawing. I'd recommend this mefhod!

 

[caruso]

Simply draw your intended route on the map connecting the dive sites and use a protractor to measure each angle and add or subtract from the current heading, updating the numbers after each wreck.

As @tursiops said the map needs to be to scale.

 

[Altamira]

Whoever drew that map needs a basic lesson in cartography. I have never seen a compass rose annotated like that. How hard is it to put N,S,E,W on the appropriate line? Before you compute any headings, you should try to determine whether or not the compass rose is correct. For example, if the vertical line on the compass rose is indeed N/S, then a 010 degree heading from the dock to the Ski Boat looks way off. If your initial heading is incorrect, you can adjust subsequent headings as long as you know the degree of inaccuracy/error to the first target/checkpoint.

 

[Dubious]

Thank you all for your quick replies. I will draw up a map based on the information from the photo.

 

[Dubious]

Whoever drew that map needs a basic lesson in cartography. I have never seen a compass rose annotated like that.

That is a picture of the sign. They have one under the pavilion and one on the dock. My guess is the map/sign is not dawn to scale but instead is meant to give visual representation. The heading given from the dock to the bus was on. That was our first stop.

 

[JackD342]

You can use Google Maps aerial view to get a more accurate image for the perimeter of the lake, and also correctly oriented. Then you can create your map to scale based on the various distance and headings from the billboard map, assuming they are accurate of course.

Also, assuming that Google is true north and your map photo is magnetic north, you can be more exact by adjusting for the local declination. Looks like magnetic north there is about -3° from magnetic north, but go ahead and double check that.

 

[BoltSnap]

I use Google Earth to do this with great accuracy. I dive from shore and I use GE to map and measure distance and compass headings to the first point and then on to the next and to the next and then back to the first or back to shore exit point. Since I got my Ratio dive computer, iX3M GPS, with GPS feature, I use it to mark GPS headings and work it with GE for verification and for more complex navigation. It works beautifully once you get the hang of it. I am sure that the GE map for locations in North America are much better in accuracy and details.

 

[Doc]

That sketch should have borne a disclaimer that it was an “artists rendering/not to scale”.

But these things serve a purpose. If they had all the headings and measurements dead nuts, there would be no learning process for navigation skills nor for a DM Candidate to complete their Dive Briefing module.

If you look hard at that sketch, there’s plenty of initial clues and notations to work with, to build on to create your own, much more complete dive site map. There’s some easy targets, quite completely findable, then some slightly less defined. Then there’s some real unknowns out there to discover.

The off-scale and goofy compass rose was likely quite intentional.

Looks like an introduction to exploration.