- Relief Displacement
- Terms
- Perspective View
- scene viewed from single viewpoint
- photo (camera ... lens)
- Orthographic View
- every point seen directly overhead
- true horizontal position
- map
- Parallax
- apparent change in position of an object
- provides 3D perception via binocular vision
- use 2 air photos to determine height, or elevation ...
- ... how topographic (contour) maps are made
- Displacement
- shift in position on photo due to difference in height (elevation)
- Equivalent Terms
- Relief Displacement
- Planimetric Shift
- Topographic Displacement
- use 1 air photo to determine height
- Photo Datum
- reference surface (for measurements)
- base elevation of photo (typically at PP)
- Geometry
- ... yup, it's ratios ... again
- D/R = d/r ...
- D/R = h/H ...
- d/r = h/H
- Displacement (d) varies with
- radial distance from PP to top (r)
- height of object (h)
- flying Height (H)
- also focal length
- draw diagrams ...
- Conditions
- vertical air photo for geometry - no tilt
- H is known (or can be determined)
- object is vertical (no lean)
- top & bottom (i.e. a sideview) visible
- displacement large enough to measure
- object is large enough
- far enough from PP
- photo scale is "large"
- limitations?
- ability to see & measure the object
- can measure to nearest 1/2 mm
- could be out by 1/4 mm
- What it means
- Worked Examples
- height (h) of building
- d=0.45cm, r=5.95cm, H=914m
- d/r = h/H ... h = d/r * H
- height (h) of building2
- d=0.95cm, r=12.75cm, H=914m
- d/r = h/H ... h = d/r * H
- height (h) of tank
- h=?, d=1.15mm (tank), r=8.25cm, A=5200ft, E=1200ft
- d/r = h/H ... h = d/r * H
- have d & r ... H= ...
- displacement (d) of hilltop
- r=8.0cm, A=10,000ft, E(pp)=200m, E(hill)=900m
- d/r = h/H ... d = r * h/H
- have r, h= ..., H=...
- Orthophoto
- "putting the hills where they belong" (prev. example)
- rectification (rubber sheeting)
- to 'shift objects to where they belong'
- removes relief displacement
- = "photomap"
- no longer viewable in 3D
