- 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 5 - Intersection of Circle
The fifth geocache in this series will use elements from Triangulation 1 (waypoint projection), Triangulation 2 (route creation) and Triangulation 3 (proximity alert creation).
Let us imagine for a moment that we want to find the coordinates for a destination where we have only the bearing but no distance from one location, and only the distance but no bearing from another location. Individually, each value provides insufficient information to proceed. However, by combining techniques learned in previous lessons, we can confidently determine two potential solutions.
To find the points of intersection on a circle with a line by bearing:
Procedure
Before searching for this geocache, it is recommended to first solve Triangulation 4, 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 '12' and save waypoint 'T5A'. At this location, the distance to the geocache container is 211 feet.
Create a proximity alert for waypoint 'T5A' on your Garmin GPSr using a radius of 211 feet. The geocache container is located somewhere along this circumference.
Find the lamp post in this park marked with the number '27' and save waypoint 'T5B'.
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 'T5C' using a bearing of 310 degrees and a distance of 1200 feet.
Create route 'T5R' using sequence 'T5B' to 'T5C'.
Begin navigation to route 'T5R' on your Garmin GPSr and find the two locations where it intersects the proximity alert created for waypoint 'T5A'.
Mark (and save) both intersection points as waypoints 'T5F1' and 'T5F2'.
You will need to explore the area around both of these waypoints using your 'geosense' to discover which is the correct solution. A hint is provided if you need it.
Upon finding the geocache log, rename the appropriate waypoint 'T5F'.
Once located, the container does not need to be removed in order to retrieve the log sheet.
When logging this find online, please include the brand and model of the equipment used to find this geocache.
Please exercise special care when retrieving and replacing the log to prevent muggles from unintentionally discovering and potentially vandalizing the container.
You should now proceed to Triangulation 6, the final geocache in this series.