A geodetic task with a Garmin handheld

**ddabcd277** · 24th September 2013, 03:03 PM

Not many people know it but could be interesting and useful to many.

Think at the end would enter in the How To section. So here the task.

You are on the shore looking at lets say an Oil Platform:

800px Cromarty Oil Platform

and you are wondering how to determine its coordinates? By chance you have a Garmin handheld with you. So how are you going to determine its coordinates? Approximately of course.

Regards,
DD

Kanopus · 24th September 2013, 04:37 PM

Are you asking if we remember that outdoor GPS can have Sight'N Go function? Or would you like to describe how to perform triangulation with this function?

**Giomen** · 25th September 2013, 12:23 AM

Mark point (1) and determine course (1) onto Oil Platform. Go to next point on the shore and go to mind course (3) and distance to it from point (1). Mark point (2) and determine course (2) onto Oil Platform in it. Switch to calculator and resolve triangulation task with known value. Make the projection of Oil Platform point and see coordinate for it. More points would give more precision result...

Another way determine course onto Oil Platform. Then correlate three value for distance: the height of device, the length extended hand this handheld, the height of something on Oil Platform (people, helicopter, safety boats...) . And again math, math and math...

**babj615** · 25th September 2013, 02:45 AM

Something even easier that requires no math or any devices other than the Garmin GPSr:

Mark a position along the beach and save as waypoint (A).

Standing at waypoint (A), use Sight 'N Go to project a waypoint in the direction of the oil rig, selecting a distance that is clearly well beyond the oil rig. Save as waypoint (B).

Move down the beach as far a distance as possible, and save as waypoint (C).

Standing at waypoint (C), use Sight 'N Go to project a waypoint in the direction of the oil rig, selecting a distance that is clearly well beyond the oil rig. Save as waypoint (D).

Now, open the Route Manager application and select Create Route. Create a Route starting at waypoint (A), to waypoint (B), to waypoint (C), and finally finish at waypoint (D).

View the selected route on the Map screen of your Garmin GPSr, and zoom in where the route crosses over itself (near the center).

Mark a new waypoint (E) at this intersection.

Waypoint (E) is the approximate location of the oil rig.

Do I win a prize?

**ddabcd277** · 25th September 2013, 12:34 PM

He-he-he, very well! Seems I am not the first one who knows how to achieve this simple triangulation task.

I understood it before couple of days and thought it is really cool. Strange but no such function in the Garminz. And is really practical. Also the handheld needs to have an electronic compass.

Do I win a prize?

Yes, lets say a beer if we see each other some day.

Ok, so here are images depicting the explanation by babj615. Images are always better than words:

[Only registered and activated users can see links. ] [Only registered and activated users can see links. ] [Only registered and activated users can see links. ]
[Only registered and activated users can see links. ]

Maybe it is even better to be made more than two projection points so to be achived better accuracy of the crossed point.

In fact Giomen method is also applicable. But we need to take two land points at the same distance from the current position in a straight line. (determine their coordinates) We should also determine the angles to the point we want find its coordinates. Then simple calculation of the isosceles triangle needs to be perform. I will try to write it next time if someone don't do it first.

Good!

**babj615** · 26th September 2013, 08:37 AM

May I add a task?

I once was searching for a puzzle type geocache with multiple waypoints. To find the solution for the final location, the user must first find three pre-determined waypoints, each of which has a unique distance measurement associated with it. The final location is precisely the given distance from each of the original three waypoints.

Using only your Garmin GPSr, how would one plot the solution?

**ddabcd277** · 26th September 2013, 09:48 AM

With circles? The distance is the radius of each circle. The solution would be the point where the three circles cross each other. Hmmm...approximate point? Not sure which handhelds have it though...

[Only registered and activated users can see links. ]

Do I win a prize?

P.P.: GPSMAP 60CSX have it.

**babj615** · 26th September 2013, 05:42 PM

Originally Posted by ddabcd277

With circles? The distance is the radius of each circle. The solution would be the point where the three circles cross each other. Hmmm...approximate point? Not sure which handhelds have it though...

[Only registered and activated users can see links. ]

Do I win a prize?

P.P.: GPSMAP 60CSX have it.

Hmmm, did you read the complete request?

Originally Posted by babj615

Using only your Garmin GPSr, how would one plot the solution?

Your screenshot is certainly not from any Garmin GPSr.

You're process is correct, but how to complete in the field using only your Garmin GPSr?

Kanopus · 26th September 2013, 07:32 PM

Solution is exactly the same, mark 3 waypoints and add proximity alarms to them. Not all gps support this feature.

**solo_voyager** · 26th September 2013, 09:22 PM

Take a bearing on it from a known location.
Move a known distance and take another bearing.
Make it far enough to give substantially different bearings, say a 30° to 45° difference.
Two angles and one side make it a standard trig calculation to find the distance to it.
Knowing the coordinates of the locations where the bearings were taken makes it an easy task to convert the distances to a coordinate.
Formulas and/or methods should be easy to find in a Google search.

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