photogrammetry. introduction photogrammetry: the science, art, and technology of obtaining reliable...

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Photogrammetry

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Page 1: Photogrammetry. Introduction Photogrammetry: the science, art, and technology of obtaining reliable information from photographs. Two major areas: metric,

Photogrammetry

Page 2: Photogrammetry. Introduction Photogrammetry: the science, art, and technology of obtaining reliable information from photographs. Two major areas: metric,

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?

Page 3: Photogrammetry. Introduction Photogrammetry: the science, art, and technology of obtaining reliable information from photographs. Two major areas: metric,
Page 4: Photogrammetry. Introduction Photogrammetry: the science, art, and technology of obtaining reliable information from photographs. Two major areas: metric,
Page 5: Photogrammetry. Introduction Photogrammetry: the science, art, and technology of obtaining reliable information from photographs. Two major areas: metric,

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.

Page 6: Photogrammetry. Introduction Photogrammetry: the science, art, and technology of obtaining reliable information from photographs. Two major areas: metric,
Page 7: Photogrammetry. Introduction Photogrammetry: the science, art, and technology of obtaining reliable information from photographs. Two major areas: metric,
Page 8: Photogrammetry. Introduction Photogrammetry: the science, art, and technology of obtaining reliable information from photographs. Two major areas: metric,

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

Page 9: Photogrammetry. Introduction Photogrammetry: the science, art, and technology of obtaining reliable information from photographs. Two major areas: metric,
Page 10: Photogrammetry. Introduction Photogrammetry: the science, art, and technology of obtaining reliable information from photographs. Two major areas: metric,
Page 11: Photogrammetry. Introduction Photogrammetry: the science, art, and technology of obtaining reliable information from photographs. Two major areas: metric,

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?

Page 12: Photogrammetry. Introduction Photogrammetry: the science, art, and technology of obtaining reliable information from photographs. Two major areas: metric,

Sidelap (about 30%),

Endlap (about 60%)

Page 13: Photogrammetry. Introduction Photogrammetry: the science, art, and technology of obtaining reliable information from photographs. Two major areas: metric,
Page 14: Photogrammetry. Introduction Photogrammetry: the science, art, and technology of obtaining reliable information from photographs. Two major areas: metric,
Page 15: Photogrammetry. Introduction Photogrammetry: the science, art, and technology of obtaining reliable information from photographs. Two major areas: metric,

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: S = f

H - h

• Average scale of a photograph: fH - havg

Savg =

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

Photo Scale = photo distance

map distanceX map scale

Page 16: Photogrammetry. Introduction Photogrammetry: the science, art, and technology of obtaining reliable information from photographs. Two major areas: metric,
Page 17: Photogrammetry. Introduction Photogrammetry: the science, art, and technology of obtaining reliable information from photographs. Two major areas: metric,

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)

Page 18: Photogrammetry. Introduction Photogrammetry: the science, art, and technology of obtaining reliable information from photographs. Two major areas: metric,
Page 19: Photogrammetry. Introduction Photogrammetry: the science, art, and technology of obtaining reliable information from photographs. Two major areas: metric,

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 :

d = r hH

where: r is the radial distance on the photo to the high pointh : 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.

Page 20: Photogrammetry. Introduction Photogrammetry: the science, art, and technology of obtaining reliable information from photographs. Two major areas: metric,

ra/R = f/H

rb/R = f/(H-h)

Then from (1) and (2);

Or

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

(rb* H) – (ra*H) = rb h

d = rb - ra = rb *hb /H

Now, what about b and c?

What would dc wrt b equals?

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

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

Page 21: Photogrammetry. Introduction Photogrammetry: the science, art, and technology of obtaining reliable information from photographs. Two major areas: metric,

Or, in general:di = (ri * hti) / (flying height above ground = H – hi)

Page 22: Photogrammetry. Introduction Photogrammetry: the science, art, and technology of obtaining reliable information from photographs. Two major areas: metric,

Flying Height of a Vertical Photograph• Flying height can be determined by:

– Readings on the photos– Applying scale equation, if scale can 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.