LESSON ON PHOTOGRAMMETRIC PROCEDURES PART 3

NUMBER OF PHOTOGRAPHS NECESSARY TO COVER A GIVEN AREA

In the preliminary estimate, the
number of photographs required is calculated by dividing the total area to be
photographed by the net area covered by a single photograph.

Let       A = total area to be
photographed.

            l = length of the photograph in the
direction of flight

            w = width of the photograph normal to
the direction of flight

            s = scale of photograph =



















 (i.e., 1 cm = s metres)

            L = net ground distance corresponding to
l

            W = net ground distance corresponding to
w

            a = net ground
area covered by each photograph = L x W

P_t = percentage overlap
between successive photographs in the direction of flight (expressed as a
ratio)

P_w = side lap (expressed as a
ratio).

Since each photograph has a
longitudinal lap of

 the actual
ground length (L) covered by each photograph is given by

                       

                                                                          (43)

Similarly, the actual ground with
(W) covered by each photograph is
given by                               

                                                                     (44)

Hence the ground area (a) covered
by each photograph

           

                (45)

The number of the photographs (N) required is given by      

N = A/a                                                                        (46)

If, however, instead of the total
area A, the rectangular dimensions (i.e., length and width) of the ground
are given, the number of the photographs required are computed by calculating
the number of strips and the number of photographs required in each strip and
multiplying the two.

Let       L₁ =
dimension of the area parallel to the direction of flight

            L₂ = dimension of the area
normal to the direction of flight

            N₁ = number of photographs in
each strip

            N₂ = number of strips
required

            N = total number of photographs to cover
the whole area.

Now net length covered by each
photograph = L = (1 – P_l) sl

  Number of photographs
in each strip is given by

           

                                                     (47)

Similarly, net width covered by
each photograph = W = ( 1 – P_w)
sw

Hence the number of the strips
required are given by

           

                                                  (48)

Thus, the number of photographs
required is

           

              (49)

google-site-verification=2j8Us0psP3GGjD12h0fH6_Z08_sRyWQjNbWcaMV4E9A