PhotogrammetryCont.

Stereoscopic Parallax The apparent displacement of the position of an object wrt a

frame of reference due to a shift in the point of observation, try it.

The shift is along the line of movement. The closer the object to the frame, the larger the shift for the

same shift, so parallax is a function of height. Parallax equations:

H-h = BfP

Parallax = p = x - x1

What is (x) ?get the flying heightor point elevation

X = Bp x Y = B

py

get ground coordinates

Stereoscopic Viewing The theory of

stereoscopic viewing and parallactic angles

Conditions for viewing a stereo model

Stereoscopic Plotters To compile maps, take cross sections, and DEM Three main components:

– Projection system– Viewing system– Tracing system

Major Types: – Optical, mechanical.– Analytical, and softcopy systems: mathematical model, require

computers

Orthophotos

Orthographic projection of photographs. Uniform scale, no relief displacement. Serve as maps Produced by “rectifying “ the photographs,

now mainly through “digital image processing”.

Advantage of orthophotomaps

Orthophoto of Washington, DC

Ground Control for Photogrammetry Each model requires three horizontal and four

vertical control points. Control points are chosen before (marked) or

after (usually) and measured by ground surveying

Using “Aerial Triangulation” control can be intensified on the photos

GPS may eliminate the need for ground control.