2.  Introduction
 Advantages
and Uses of orthophotos
 Classification
of Instruments

3.  Ortho-photos
are
Orthographic
photographs
 They
do not contain
the scale, tilt and
relief distortions .
 Ortho-photos
(images of features)and
maps(utilizes lines and symbols) are similar

4.  Ortho-photos
are produced from perspective
photos through a process called differential
rectification
 Which
eliminates image displacements due to
photographic tilt and relief
 Perspective
must obviously be removed, but
variations in terrain should also be corrected
 Multiple
geometric transformations are applied
to the image, depending on the perspective
and terrain corrections required on a particular
part of the image.

7. 
Orthophotos can be used as maps for making direct
measurements of directions, angles, positions and area.

Orthophotos have the pictorial qualities of air photos because
the images of an infinite number of ground objects can be
recognized and identified.

Orthophotos are used as base-maps for plotting field
observation

Using orthophotos , engineers are better able to
communicate with property owners to discuss right- of-way
purchase, access to property etc.

Ortho-photos are commonly used in geographic information
systems, such as are used by mapping agencies

8. 1.Those which produce images by direct
optical projection
2.Those which produces images
electronically

9. 
A 6 inch ( 150mm) focal length camera should be used.

End lap (60%)and side lap(30%) for orthophotography
should generally be about as same as that for mapping
photography .