Triangulation 2 Multi-Cache

• The intent of this series of geocaches is to help us learn how to apply triangulation techniques to find the location of unknown points using a handheld GPSr.
• While these geocaches were created and tested using a Garmin GPSr, they can also be found using a smartphone or other device with the appropriate software.
• It is recommended to find this series of geocaches in numerical order (1-6) as each geocache builds on techniques and information learned in previous finds.

The Oxford dictionary defines Triangulation as "(in surveying) the tracing and measurement of a series or network of triangles in order to determine the distances and relative positions of points spread over a territory or region, especially by measuring the length of one side of each triangle and deducing its angles and the length of the other two sides by observation from this baseline."

In practice, 'Triangulation' is actually a generic term commonly used when referring to several surveying terms:

• Triangulation refers to the process of determining the location of a point by forming triangles to it from known points, using only angle measurements.
• Trilateration (True Range Multilateration) is a method of determining the location of a point using multiple known distance measurements from known points.
• Triangulateration involves the use of both angle and distance measurements to determine the location of a point.

To find the final location of each geocache in this series, we will actually be using Triangulateration, which is a combination of both Triangulation and Trilateration.

Additional information can be found at GPSrChive > How To... > Triangulation.

While the procedures provided in this geocache series are not mutually exclusive, and exploring additional techniques to solve each problem is encouraged, please be mindful of accuracy limitations imposed when using consumer grade equipment to perform these exercises.

Triangulation 2 - Intersection by Projection

The second geocache in this series will use elements from Triangulation 1 (waypoint projection) and route creation.

This navigation technique is primarily useful for determining the approximate location of a distant waypoint or landmark within visual range (tree, hilltop, cave entrance, windmill, flag pole, etc.). By measuring the bearing from two known locations to a desired landmark and then creating routes along those paths via waypoints projected beyond the target destination, we can create a virtual 'X marks the spot' right on our GPSr map display.

Creating a Route using a Garmin GPSr:

1. Open Route Planner page
2. Select 'Create Route'
3. Choose 'Select First Point'
4. Select 'Waypoints'
5. Choose desired waypoint
6. Select 'Use'
7. Choose 'Select Next Point'
8. Select 'Waypoints'
9. Choose desired waypoint
10. Select 'Use'
11. Repeat Steps 7-10 for each additional waypoint
12. Select 'Back' or 'Exit' to save the route

To find the coordinates for an unknown waypoint where two locations and bearings are known:

 

Procedure

Before searching for this geocache, it is recommended to first solve Triangulation 1, the previous geocache in this series.

Configure your GPSr heading to use True North.

Configure your GPSr routing method to use Direct Routing.

Find the lamp post in this park marked with the number '14' and save waypoint 'T2A'.

Here we know the bearing to a landmark (the geocache), but we do not know the actual distance, so we will project a waypoint using a distance value we believe to be approximately twice that to the landmark.

Project (and save) waypoint 'T2B' using a bearing of 231 degrees and a distance of 1500 feet.

Find the lamp post in this park marked with the number '28' and save waypoint 'T2X'.

Again, we know the bearing to a landmark (the geocache), but we do not know the actual distance, so we will project a waypoint using a distance value we believe to be approximately twice that to the landmark.

Project (and save) waypoint 'T2Y' using a bearing of 267 degrees and a distance of 1500 feet.

If we can determine where the previous two projections cross paths, we will have the approximate location of the targeted landmark.

Create route 'T2R' using sequence 'T2B' to 'T2A' to 'T2X' to 'T2Y'.

Begin navigation to route 'T2R' on your Garmin GPSr and find the location where it intersects itself.

Mark (and save) the route intersection as waypoint 'T2F'.

Upon arrival at waypoint 'T2F', put down the GPSr and use your 'geosense' to find the geocache container.

Once located, the container does not need to be removed in order to retrieve the log sheet.

Please exercise special care when retrieving and replacing the log to prevent muggles from unintentionally discovering and potentially vandalizing the container.

When logging this find online, please include the brand and model of the equipment used to find this geocache.

You should now proceed to Triangulation 3, the next geocache in this series.