Vertical distances will be measured by leveling instruments as it would be impossible for surveyors to use the tape to do the procedure. In order to have a hands-on real idea on how the procedure is gone through, students are given the dumpy level in order to focus on just the vertical measurement right after horizontally leveling the telescope.
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| courtesy of John A. Dutton e-Education Institute |
The preliminary study lies on the definition of terms which would be encountered in the procedures. The route will be divided into segments and each of these stations may either be called the following:
1. Benchmarks - the stations which are of more importance to the procedure. Most often in the field work, students will be using only two benchmarks (BM-1 and BM-2) although, in practice there is not any limitation of setting out the number of benchmarks in surveying.
2. Turning Points - stations similar with BMs, however, these are stations with lesser importance. They were set up in order to have equally divided segments along the course.
The procedure covers students to read elevations from two stadia rods, one at the point of origin and the other as they move to the point of destination.
1. Backsight reading - the elevation reading from the point of origin.
2. Foresight reading - assuming students determined the flow of surveying, this is the elevation reading going to the point of destination.
3. Intermediate foresight readings - there are leveling methods whereby other readings are taken surrounding the course. These readings are used to map out the terrain of the area.
Different leveling techniques shall be used based on accuracy of data, the purpose of surveying, or the terrain of the area. The most basic is Differential Leveling in which the course are set out and students simply take backsight and foresight readings on field. The different alterations of this method are:
a. Double-rodded which uses two stadia readings (lower and higher) to make more precise elevation data.
b. Three-wire which makes use of the different hairs observed inside the eyepiece (upper hair, crosshair, lower hair).
When the surveyors are more concerned with the topography of the area, they implore the other methods of leveling:
a. Profile leveling in which they need to take numerous intermediate foresight readings to plot out the configuration of the surrounding terrain.
b. Rise and fall method is a similar surveying procedure as profile leveling however, the computation depends on the discrepancy of elevations thus rise or fall.
Reciprocal leveling is used specially if the elevations to be determined are on points laying between ravines or wide rivers. Since this situation will not allow surveyors to have readings on the water or ravine, they need to implore a different working method both on field procedure and computation.
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