m8 Measurement of vertical distances

Differential Leveling

It is a process used to find the difference in elevation between two or more points that are far apart.

Benchmark

It is a fixed reference point whose elevation is either known or assumed.

Permanent Benchmarks

These are established at intervals by agencies like the Philippine Coast and Geodetic Surveys (PCGS) or the Bureau of Lands and are determined using precise leveling methods. They serve as reliable points of reference for levels in a given area.

Temporary Bench Marks

These are set up by a surveyor for use on a specific project and may have assumed elevations.

Backsight

It is a rod reading taken on a point whose elevation is either known or assumed. It is always the first rod reading taken after the leveling instrument has been set up and leveled.

Foresight

It is a rod reading taken on a point whose elevation is to be determined. It represents the vertical distance from the instrument's line of sight down to the point where the rod is held.

Backsight Distance

It is measured from the center of the instrument to the rod on which a backsight is taken.

Foresight Distance

The horizontal distance from the center of the instrument to the rod on which a foresight is taken

Turning Point

It is also known as a change point (CP), is an intermediate stable point used in leveling to allow the operation to continue from a new instrument setup.

Height of Instrument

It is the elevation of the line of sight of an instrument above or below a selected reference datum.

Station

This is the point on which the rod is held (e.g., a BM or TP), not the location of the instrument.

Backsight

The rod reading taken on a point of known elevation (added to Elev to get HI).

Height of Instrument

The computed elevation of the instrument's line of sight ($\text{Elev} + \text{BS}$).

Foresight

The rod reading taken on a point of unknown elevation (subtracted from HI to get Elev).

Elevation

The computed elevation of the point where the rod is held ($\text{HI} - \text{FS}$).

Left-Hand Page

Used for recording observed and computed numerical data.

Right-Hand Page

Reserved for sketches, descriptive notes, and remarks about Benchmarks (BMs) and Turning Points (TPs) for future reference.

Header

Should include the date and time of the survey, average temperature, and weather conditions.

Arithmetic Check

A crucial part of the process is the arithmetic check, which confirms the accuracy of the additions and subtractions.

Authentication

The field notes must be authenticated with the signature of the chief of party.

Profile Leveling

Itis the process of determining differences in elevation along a fixed line at short, measured intervals to create a vertical cross-section of the ground.

Profile

It is a curved line which graphically portrays the intersection of a vertical plane with the surface of the earth.

Stationing

A numerical designation given in terms of horizontal distance any point along a profile line is away from the starting point.

Intermediate Foresights

These sights, which are also known as ground rod readings, are taken along the centerline of the proposed project to provide an accurate representation of the ground surface.

Full Stations

Are points which are established along the profile level route at uniformly measured distances.

Plus Stations

Any other intermediate point established along a profile level route which is not designated as a full station is called a plus station.

Vertical Exaggeration

It is a process of drawing the vertical scale for a profile much larger than the horizontal scale in order to accentuate the differences in elevation.

Profile Paper

A special heavy grade graphing paper used for plotting profiles.

Plotting Scales

The horizontal and vertical scales used in plotting the profile should be properly identified.

Stationing

The full stations along the level route should be indicated to portray the overall linear length of the line.

Reference Points

Important reference points and other ground points which need to be emphasized or pointed out should be easily seen.

Marginal Information

Any other valuable information which should explain the profile better or in detail should be indicated.

Trigonometric Leveling

It is also known as indirect leveling, is a method used to determine the difference in elevation between points by measuring the vertical angle and either the horizontal or inclined distance between them.

Reciprocal vertical-angle observation

The effects of curvature and refraction can be eliminated if vertical angle observations are made simultaneously at both ends of the line such as points A and B.

Inverse Leveling

It is sometimes necessary to determine the elevation of a point located higher than the telescope of the instrument. In such situations, the rod is held upside down and its base is placed up at the desired point.