Phototheodolite: It is a combination of “theodolite and a terrestrial camera.
Important parts are:
Important Definitions
Horizontal and Vertical angles from terrestrial photograph
Ob' = fsecα_{b}
X_{a} = tanα_{a}y_{a} = Oa'tanβ_{a} = fsecα_{a} = fsecα_{a}.tanβ_{a}
X_{b} = tanb_{a}y_{b} = Oa'tanβ_{b} = fsecα_{b} = fsecα_{b}.tanβ_{b}
tanα_{a} = X_{a}/f
tanα_{b} =X_{b}/f
tanβ_{a} = y_{a}/fsecα_{a}
tanβb = y_{b}/fsecα_{b}
Angle φ_{1} is magnetic bearing of camera axis (or principal vertical plane.)
Azimuth of line Ok = φ_{1}
Azimuth of line OA = φ_{1}  α_{a }(OA is left to OK)
Azimuth of line OB = φ_{1}  α_{b} (OA is right to OK)
So, Azimuth of a line = Camera azimuth + α
Elevation of a point by photographic measurement
Consider Point A
tanα_{a} = X_{a}/f
If V = Elevation of point A above Horizontal plane through camera axis.
From Similar triangle
Elevation of point A.
h = H_{C} + V + C
Where, H_{C} = Elevation of camera
V = Elevation of point A
C = Correction for curvature and refraction.
h = H_{C} + V + C
Arial photograph are taken from a fast speed arial camera which have very high speed and efficient shutter, using high speed emulsion for the film.
Important Definitions
Relation between principal point, plumb point and isocentre
Scale of a Vertical Photograph
Scale varies for points of different elevation, scale will be constant only when elevation of all points are same.
If all the points are on the same elevation.
Then
Scale S = Map distance/Ground distance = ka/KA
Case 2: If A and B are two points having elevation h_{a} and h_{b} respectively above mean sea level. Scale of photograph at elevation h_{a}.
Scale of photograph at elevation h_{b}.
So in general scale of photograph for different elevations (h).
S_{h} = f/(Hh)
This can be represented by representative fraction (R_{n}) also.
Different Scales
Relief Displacement
Due to different elevation of different points, every point on photograph is displaced from their original position. This displacement is called relief displacement.
r = K_{a}
r_{o} = K_{a}_{o}
R = K_{o}A_{o}
aa_{0} is called relief displacement.
aa_{0} = r  r_{o}
from similar triangle.
So relief displacement
So relief displacement
If relief displacement is known then height of an object
h = dH / R
19 videos31 docs35 tests

1. What is photogrammetric surveying and how is it used in civil engineering? 
2. What are the advantages of using photogrammetry in civil engineering surveys? 
3. What are some common applications of photogrammetry in civil engineering? 
4. What are the key steps involved in a photogrammetric surveying process? 
5. What are some challenges and limitations of photogrammetric surveying in civil engineering? 

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