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:– See the same point from

two

locations

Separately

At, or almost at, the same time.

Animation Showing June 3, 2004 Meteor Path Over WACourtesy of Marco Langbroek & Others

from http://www.visualizationsoftware.com/3dem/oldflybys.html, courtesy of : Richard Horne

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.

Integrated technology

Photogrammetry systems are installed into Total stations and LIDAR system to suppplement and add to the data collected.

For example, LIDAR provides clouds of points (XYZ), their color is taken from the RGB value of the pixel at the same location in the photograph.

Examples