1.22.5. Triangulation survey work

It involves two major steps; (i) Field work, and (ii) Computational work.

Triangulation survey work is divided into two primary phases: field work and computational work. The field work encompasses the actual practice of surveying on-site, while the computational work involves processing the collected data to produce usable results.

Think of the field work like taking measurements while building a house—you're checking dimensions and making sure everything is in the right place. The computational work is akin to drafting the blueprints based on those measurements to ensure that you have a clear plan moving forward.

The field work involves (a) Reconnaissance survey, (b) Erection of signals, (c) Measurement of starting baseline, (d) Measurement of horizontal and vertical angles, (e) Observations to determine the azimuth of sides, and (f) Measurement of closing baseline.

The field work consists of several key activities: 1. A reconnaissance survey helps in understanding the area better and planning the triangulation layout. 2. Erection of signals marks the locations for observation. 3. Measuring the starting baseline is critical as it forms the basis for triangulation. 4. Measuring horizontal and vertical angles allows for the precise calculation of positions. 5. Observations to determine the azimuth are necessary to know the direction of the sides of triangles formed. 6. Finally, the closing baseline is measured to check accuracy and ensure all points are connected properly.

Imagine planning a treasure hunt in a park. First, you would walk around to see where to hide clues (reconnaissance survey). Next, you mark the spots where the treasure is hidden with flags (signals), then you would start measuring distances from point to point (baseline), observing directions (angles), and finally ensuring you can get back to the starting point to verify you haven't got lost (closing baseline).

The computational work includes: • Checking the observed angles • Checking the triangulation errors • Checking the closing horizon error at each station (i.e., sum = 3600) • Computation of corrected length of baseline • Computation of sides of triangles • Computation of the latitude and departure of each side of the triangulation network, and • Computation of independent coordinates of the triangulation stations.

In the computational stage, the first step is to check the angles observed during the measurements to confirm their accuracy. Next, any errors found in the triangulation process need to be accounted for and corrected. Each station should also indicate a total horizon error of 360°, ensuring the angles form a closed loop. Following this, the length of the baseline is corrected to reflect actual measurements, which leads to calculating the lengths of triangle sides, as well as the latitude and departure for each side. Finally, independent coordinates of all triangulation stations are computed to determine their exact locations.

This stage is comparable to a chef checking the recipe after a meal is prepared (checking angles) to ensure everything was measured correctly. They might taste the dish (checking errors) and adjust ingredients accordingly (correcting baselines). Before serving, they ensure all flavors blend well together (checking closing error), and finally, they record which ingredients and quantities were used (calculating coordinates).

The reconnaissance of the area involves; (i) proper examination of the terrain, (ii) selection of suitable positions for baselines, (iii) selection of suitable positions of triangulation stations, and (iv) determination of intervisibility of triangulation stations.

During reconnaissance, surveyors examine the landscape to understand its features, which helps in determining the best locations for baselines and triangulation stations. It is crucial for the bases to be visible from one another; this is known as intervisibility. Each of these actions ensures that the survey can be conducted accurately.

This process can be likened to planning a hiking route. Before starting, hikers will look at maps and the terrain (examining the landscape) to choose the best trails (selecting positions). They will also ensure that the next point on the trail is visible from the current point (intervisibility), to avoid getting lost.

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