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Photogrammetry






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Photogrammetry. Introduction. Photogrammetry: the science, art, and technology of obtaining reliable information from photographs. Two major areas: metric, and interpretative. Terrestrial and aerial Photogrammetry.
Photogrammetry

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PhotogrammetrySlide 1

Photogrammetry

IntroductionSlide 2

Introduction

  • Photogrammetry: the science, art, and technology of obtaining reliable information from photographs.

  • Two major areas: metric, and interpretative.

  • Terrestrial and aerial Photogrammetry.

  • Uses of Photogrammetry: topographic mapping, determine precise point coordinates, cross sections, deflection monitoring, and many other applications.

  • Why Photogrammetry?

Aerial camerasSlide 5

Aerial Cameras

  • For precise results, cameras must be geometrically stable, fast, have efficient shutters, sharp lenses

  • Single-lens frame cameras: figure 27-2

    • most used format size is 9”, focal length 6 in

    • components: lens, shutter, diaphragm, filter, focal plane, fiducial marks.

    • shutters can be operated manually or automatically.

    • The camera could be leveled regardless of the plane orientation.

    • Exposure station and principal point.

    • Camera calibration.

Aerial photographsSlide 8

Aerial Photographs

  • True Vertical: if the camera axis is exactly vertical, or near vertical.

  • Tilted Photographs

  • Oblique photographs: high and low

  • Vertical Photos are the most used type for surveying applications

Geometry of vertical photographsSlide 11

Geometry of Vertical Photographs

  • Figure 27-6

  • Define: image coordinate system (right handed), principal point, exposure station.

  • Measurements could be done using negatives or diapositives, same geometry.

  • Strips and Blocks.

  • Sidelap (about 30%), and Endlap (about 60%), why?

Scale of a vertical photographSlide 15

Scale of a Vertical Photograph

  • Figure 28-6

  • Scale of a photograph is the ratio of a distance on a photo to the same distance on the ground.

  • Photographs are not maps, why?

  • Scale of a map and scale of a photograph.

  • Orthphotos

  • Scale (s) at any point:

f

S =

H - h

f

  • Average scale of a photograph:

Savg =

H - havg

If the f, H, and h are not available, but a map is available then:

photo distance

X map scale

Photo Scale =

map distance

Ground coordinates from a single vertical photographSlide 17

Ground Coordinates from a Single Vertical Photograph

  • Figure 27-8

  • With image coordinate system defined, we define an arbitrary ground coordinate system.

  • That ground system could be used to compute distances and azimuths. Coordinates can also be transformed to any system

  • In that ground system:

    Xa = xa * (photograph scale at a)

    Ya = ya * (photograph scale at a)

Relief displacement on a vertical photographSlide 19

Relief Displacement on a Vertical Photograph

  • Figure 27-9

  • The shift of an image from its theoretical datum location caused by the object’s relief. Two points on a vertical line will appear as one line on a map, but two points, usually, on a photograph.

  • In a vertical photo, the displacement is from the principal point.

  • Relief displacement (d) of a point wrt a point on the datum :

r h

d =

H

where: r is the radial distance on the photo to the high point

h : elevation of the high point, and H is flying height above datum

  • Assuming that the datum is at the bottom of vertical object, H is the

  • flying height above ground, the value h will compute the object height.

PhotogrammetrySlide 20

ra/R = f/H

Or: ra *H = R * f ----(1)

rb/R = f/(H-h)

Or: rb * (H-h) =R * f ---(2)

Then from (1) and (2);

Or

ra *H = rb * (H-h) then;

D = rb - ra = rb *hb /H

Flying height of a vertical photographSlide 21

Flying Height of a Vertical Photograph

  • Flying height can be determined by:

    • Readings on the photos

    • Applying scale equation, if scale could be computed

      • Example: what is the flying height above datum if f=6”, average elevation of ground is 900ft, scale is 1”:100ft? Is it 1500’?

    • Or, if two control points appear in the photograph, solve the equation:

      L2 = (XB - XA)2 + (YB - YA)2

      then solve the same equation again replacing the ground coordinates with the photo coordinates.


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