triangulation

1 a trigonometric method of determining the position of a fixed point from the angles to it from two fixed points a known distance apart; useful in navigation

2 a method of surveying; the area is divided into triangles and the length of one side and its angles with the other two are measured, then the lengths of the other sides can be calculated

English

Noun

1. A technique in surveying in which distances and directions are estimated from an accurately measured baseline and the principles of trigonometry
2. The network of triangles, so obtained, that are the basis of a map or chart
3. In navigation or seismology, a process by which an unknown location is found using three known distances from known locations.
4. A delaying move in which the king moves in a triangular path in order to force the advance of a pawn.
5. Using multiple researchers to interview the same people or to evaluate the same evidence to reduce the impact of individual bias. [ref (1)] "Triangulation was established by asking researcher #2 and researcher #4 to conduct their own interview of the participant".

Related terms

• triangulate

References

(1) (Nahid Golafshani, 2003) Understanding Reliability and Validity in Qualitative Research, The Qualitative Report Volume 8 Number 4 December 2003 597-607, http://www.nova.edu/ssss/QR/QR8-4/golafshani.pdf

In trigonometry and geometry, triangulation is the process of finding coordinates and distance to a point by calculating the length of one side of a triangle, given measurements of angles and sides of the triangle formed by that point and two other known reference points, using the law of sines.

In the figure at right, the third angle of the triangle (call it θ) is known to be 180 − α − β, since the sum of the three angles in any triangle is known to be 180 degrees. The opposite-side for this (the third) angle is l, which is a known distance. Since, by the law of sines, the ratio sin(θ)/l is equal to that same ratio for the other two angles α and β, the lengths of any of the remaining two sides can be computed by algebra. Given either of these lengths, sine and cosine can be used to calculate the offsets in both the north/south and east/west axes from the corresponding observation point to the unknown point, thereby giving its final coordinates.

Some identities often used (valid only in flat or euclidean geometry):

• The sum of the angles of a triangle is π radians or 180 degrees.
• The law of sines
• The law of cosines
• The Pythagorean theorem

Calculation

• α, β and distance AB are already known
• C can be calculated by using the distance RC or MC:

• RC: Position of C can be calculated using the Law of Sines

\gamma=180^\circ-\alpha-\beta

\frac=\frac=\frac

Now we can calculate AC and BC

AC=\frac

BC=\frac

Last step is to calculate RC via

RC=AC \cdot \sin\alpha

or

RC=BC \cdot \sin\beta

• MC can be calculated using the Law of Cosines and the Pythagorean theorem

MR=AM-RB=\left(\frac\right)-\left(BC \cdot \cos\beta\right)

MC=\sqrt

Triangulation is used for many purposes, including surveying, navigation, metrology, astrometry, binocular vision, model rocketry and gun direction of weapons.

Many of these surveying problems involve the solution of large meshes of triangles, with hundreds or even thousands of observations. Complex triangulation problems involving real-world observations with errors require the solution of large systems of simultaneous equations to generate solutions.

Famous uses of triangulation have included the retriangulation of Great Britain.

See also

• GSM localization
• Multilateration, where a point is calculated using the time-difference-of-arrival between other known points
• Parallax
• Real-time locating
• Resection
• SOCET SET
• Stereopsis
• Trig point
• Trilateration, where a point is calculated given its distances from other known points

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