# Principal Method of Terrestrial Photogrammetry

The principal is exactly similar to plan table surveying, it may be stated as βThe position of the object with ref to the base line is given by the intersection of the rays drawn to it form each end of the base lineβ In plane tabling most of the work is executed in the field while in this method it is done in the office. The principal is explained as follows

C and D = Camera stations.

CD = Base line of length βBβ

CE and DE = Position of vertical plane of collimation. and

B = Observed vertical angles which the vertical plane of collimation make with base line at C and D.

M = pt to be located, which is shown as βmβ in both the photographs.

X1 and Y1 = Coordinates of βMβ on ptβCβ

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X2 and Y2 = ----------------------------βDβ

F = focal length of camera lens

(Photograph from βCβ) (Photograph from βDβ)

## Method of location PT βMβ:

Pt βMβ may be plotted graphically or analytically.

## Graphical Method :

- First plot the base line to the given scale

- Draw CE making an angles of β β wide CD with the help of a protector.
- Similarly draw DE making an angle of B with BE.
- On CE mark the pt βeβ at a distance equal to fine font of βCβ. Similarly setoff a distance βDeβ equal to βfβ along DE in front of D as shown.
- To these pts and βeβ draw lines right angles ot CE and DE respectively measure βemβ equal to X1and To X2 along these perpendicular lines on the same side as on the photographs. (Her they are measured on ht left of CD and DE)
- Join βCMβ and βDMβ and produce them so as to meet at βMβ which gives required position of βMβ on Plane
## To determine the level of PT βMβ

- Measure βyβ which gives the height of βmβ above the horizontal hair. Rise of the ray from βmβ to the center of the object glass is equal to βyβ in a horizontal dist
- Measure the distance βCMβ to the scale on the plane.

- The height βHβ of βMβ above the horizontal Plane of collimation at βCβ is given by Knowing the reduced level (RL) of horizontal plane of collimation, the RL of M may be obtained as R.L of M= R.L of horizontal plane of collimation at 'C' is given by:

## Field Work:

The field work of terrestrial photographic surveying consists of

- Reconnaissance

- Triangulation

- Camera work