GEOL 102 Lecture 9: Gemstones Lecture
31 Oct 2017
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Document Summary
Principal point the centre of the air photo. Marked by a cross and connecting fiducial marks (notches on sides) Scale = focal length/height above ground s=1/sf where sf is the scale factor. Focal length and height above ground are either given, or found on the air photos. Focal length typically given in inches or mm. Scale from photo to topo map: sp=sm*dp/dm; dm=distance on map, dp=distance on photo, sm=scale of map(known). All the distances are the distance between 2 points on their respective images. For effect of tilt and focal length refer to photography and terrain. Measuring heights from single photo: h=(dp/r)*h: h=height of object, h=elevation of plane above ground, r=distance from top of object to centre of photo, dp=radial displacement(apparent length of tilted feature) Shadows: h=l*tan(a): a=elevation of sun(angle), l=length of shadow, h=height of object is the base of the object. (avg distance from base to middle of photo).
