different methods of height measurement from Aerial Photograph

1. HEIGHT MEASUREMENT FROM AERIAL PHOTOGRAPH
Presented By:
Avijit Ghorai
M.Sc in Geography
Vidyasagar University

2. 1. What is the Aerial Photo?
2. Geometric Types
3. Vertical Aerial Photograph
4. Geometry and components of vertical photograph
5. Height measurement of Aerial Photograph
CONTENT
• Height measurement based on Relief Displacement
• Height measurement based on Shadow length
• Height measurement based on Stereoscopic parallax

3. What is Aerial Photo?
Aerial photography (or airborne imagery) is the taking of photographs from an
aircraft or other flying object.
Platforms for aerial photography include fixed-
wing aircraft, helicopters, unmanned aerial vehicles (UAVs or
"drones"), balloons, rockets, kites, parachutes,
Aerial photography was the first method of Remote sensing and even used
today in the era of satellite and electronic scanners. Aerial photographs will still
remain the most widely used type of Remote Sensing Data.

4. 1. Vertical aerial photograph:
- camera Tilt <3⁰ from the vertical
2. Low oblique Aerial Photograph:
-inclined about 30° from the vertical
3. High oblique Aerial Photograph:
-camera inclined about 60° from the
vertical

5. Taking Vertical Aerial Photographs
Most vertical Aerial photographs are taken with frame cameras along flight lines. The line traced on
the ground directly beneath the aircraft during acquisition of photography is called the ‘Nadir line’.
This line connects the image centres of the vertical photographs.
Fig: photographic coverage along a flight strip: a)condition during
exposure, b)resulting photography
Each vertical aerial photograph overlaps the next photograph in the flight line by approximately
60%(referred to as stereoscopic overlap). And the sidelap require 20-40%. This overlap is very
important because it provides at least two and some times three photographic view of each object in
the real world along a flight line.

6. Fig: Geometry of vertical aerial photo
Source: Elements of Photogrammetry with application in GIS, 4th edition,
2014 McGraw Hill
Fig: components of vertical aerial photo
Source: HTTPs://slideplayer.com/slide/7533210/

7. Height Measurement of Aerial Photography
Method:1
Displacement is shift in the location of an object
in a photo, which does not change the
perspective characteristics of the photo..
Source:
https://www.google.co.in/search?q=height+measurement+from+relief+displaceme
nt&rlz=1C1GCEA_enIN787IN787&source=lnms&tbm=isch&sa=X&ved=0ahUKEwi0uf-
D1ZHeAhUXEnIKHWotDnUQ_AUIDigB&biw=1536&bih=754#imgrc=sV3kAkvRVSxKo
M:

8. Causes of Relief Displacement
The amount of relief displacement depends upon:
A. Height of the Object:
When the distance of objects from the nadir point is
remain same. But the object height increased or
decreased.
Higher object is more displaced.

9. B. The distance of the objects from nadir point
When the distance of object is more from nadir point,
the relief displacement will be more.
C. Focal Length
When the focal length of camera lens is
increased, the
relief displacement will be more. On the
other hand, when
the focal length of camera lens is
decreased, the relief
displacement will be less.

10. D. Flying height or altitude
If the focal length of the camera lens remain
constant. When the flying height increased, the
relief displacement will be decrease.
E. The height of the object in relation to datum plane

11. F. Effect of the field of view
Normal angle of view will result in smaller relief
displacement (shift on the photograph of a point because of
its relief (height).

12. Height Measurement From Relief Displacement
d= Relief Displacement, r= Radial distance from principle
point to top or the displaced object/displaced image point,
h= object height, H= Flying height above the datum, R=
Ground Radial Distance.
h/H = d/r
Or, d=r*h/H
Or, h=d*H/r

13. Method: 2
Source:
https://www.google.co.in/search?q=Height+Measurement+Based+on+Shadow+Length+of+aerial
+photo&rlz=1C1GCEA_enIN787IN787&tbm=isch&source=lnms&sa=X&ved=0ahUKEwiY-
Ozq25HeAhUYFHIKHZifBl0Q_AUICigB&biw=1396&bih=686&dpr=1.38#imgrc=KwADsqxBzEdJtM:
Formula:
tan e =height(H) / Shadow length(L)
Or, H=L*tan e
The tower on the nearby parking
structure, the shadow length is 20feet
and angle(e) is 30⁰. So the height of
the object is..
h=L*tan e
=20’*tan 30⁰
=11.547feet.

14. Method: 3
 Parallax is the apparent displacement in the position
of an object.
 Parallax is caused by taking photograph of the
same object but from different point of observation.
Types:
1. Differential Parallax
2. Absolute Parallax Source: http://www.ccrs.nrcan.gc.ca/ccrs/learn/
tutorials/stereosc/chap4/

15. 1. Differential Parallax:
The difference between the
stereoscopic parallax at the top and
base of the object.
D.P=15.2mm. - 13.5mm.
=1.7mm:

16. 2. Absolute Stereoscopic parallax:
Absolute stereoscopic parallax: the
average photo base length = average
distance between PP and CPP
• PP = Principal point = centre of photo
• CPP = Conjugate principal point = adjacent
photo’s PP

17. Computing height using stereoscopic parallax
where,
h = object height
H = flying height
dP = differential parallax
b = average photo base length(absolute parallax)
h = (H) * dP / (b + dP)

18. Bibliography
 Jensen, john R. (2004).Remote Sensing Of the Environment.2nd ed. Singapore: Pearson,137-178.
 Lillesand, Thomas M. Kiefer, Ralph W. and Chipman,Jonathan W.(2014).Remote Sensing And Image
Interpretation.6th ed.New Delhi:Wiley,123-145.
 Devi,Sunita,Veena.(2014).Measurement of Relief Displacement from Vertical Photograph. International Journal of
Science, Engineering and Technology Research (IJSETR),3(10).

19. Thank You