4/30/2015 GEM Lecture 13 Content Orientation –Inner –Relative –Absolute

4/30/2015 GEM Orientation The formation of a stereo model to simulate the perspectives of the aerial camera at the time of exposure is by no means automatic, a strict ‘setting-up’ procedure must be followed Each lamp on a traditional stereoplotter has to be focused and centered in order to project a close to perfect perspectives of light rays. This process is called “inner orientation”

4/30/2015 GEM PROJECTION SYSTEM – –Light rays projected through projector objective lenses and intercepted below on platen – –Requires operation in dark room – –Lens formula must be satisfied 1/f = 1/p + 1/h – –Intersection must occur within depth of field of projector lens

4/30/2015 GEM Inner (Or Interior) Orientation The purpose of inner orientation is to recreate the geometry of rays at the time of exposure The procedure described here is with reference to an analogue stereoplotter Inner orientation involves: – –Correctly centering the two photographs using the fudicial marks in the stereoplotter to exactly locate the principal point – –Introduce the focal length distance in the instrument

4/30/2015 GEM Relative Orientation – –The purpose of relative orientation is to re-create a stereo model of terrain in a smaller scale such that parallax is minimized – –Choose six readily discernable image points approximately in the positions shown below: Photo 1 Photo 2 Points 1 and 2 are near the principal points of photos 1 and 2

4/30/2015 GEM – –The image processing method of relative orientation uses image processing to compare pixel groupings on the left and right photos and determine relative points from matched sets – –The two-image selection method of relative orientation offers selection of points appearing in the overlap area of only the two open images For the selection method of relative orientation, select relative points, remove parallax, and digitize each point

4/30/2015 GEM – –Each projector is capable of six movements: Translations – x, y, z Rotations – ω, φ, κ κ axis BxBx ByBy BzBz ω axis Φ axis

4/30/2015 GEM Omega, Phi and Kappa define the orientation of the sensor when the imagery was captured. X Y Z Phi+ Y is principle & Phi (+) X-axis Y-axis Z-axis Omega Phi Kappa Phi- Y X Z Y is principle & Phi (-) This format of Omega, Phi, Kappa is the most commonly used convention (ISPRS)

4/30/2015 GEM To eliminate the parallax at the 6 points (using an analogue stereoplotter) the following relative orientation task is done: i. i.At point 1 by swing of projector 2 ii. ii.At point 2 by swing of projector 1 (Repeat i and ii until points 1 and 2 are free of parallax) iii. iii.At point 6 by tip of projector 1 iv. iv.At point 4 by tilt of projector 1, over tilt by imparting about three times the amount of tilt required to remove parallax (Repeat until points 1,2,4 and 6 are free of parallax) v. v.At point 5, tip projector 2. Check for parallax at point 3, and repeat all movements until parallax is removed from all six points

4/30/2015 GEM bxbxbxbx bybybyby bzbzbzbz dωdωdωdω dφdφdφdφ dκdκdκdκ Photo 1 Photo Photo 1 Photo Photo 1 Photo Photo 1 Photo Photo 1 Photo Photo 1 Photo 2

4/30/2015 GEM Each projector has six motions, giving 12 motions for the stereopair Relative orientation on an analogue stereoplotter usually require fifteen to sixty minutes to be completed (depending upon the experience of the operator)

4/30/2015 GEM Absolute Orientation The purpose is to bring the model to the desired scale and introduce the ground control information After inner and relative orientation the stereomodel is geometrically similar to the terrain but it must be brought to a known scale through the introduction of ground control – –Achieved by: By changing the distance between the projectors Tilting the projectors together so that elevations are correctly measured

4/30/2015 GEM – –The analogue stereoplotter need to be scaled and leveled – –The required corrective rotation is resolved into two components ω and φ – –Minimum of three control points are required – –In the analogue stereoplotter this is a manual iterative process (being careful not to disturb the relative orientations) – –Can take between 2 to 3 hours to get done

4/30/2015 GEM Exterior Orientation Exterior orientation is the process of gathering enough information about individual images to be able to calculate the ground coordinate of each image center The interior and relative orientations provide the information necessary to calculate exterior orientation Exterior orientation is usually calculated by a third-party aerotriangulation (AT) software package

4/30/2015 GEM Height Measurements Achieved using the cursor in the stereo model Location of point (X,Y & Z)

4/30/2015 GEM Height Measurements Location of point (X,Y & Z )

4/30/2015 GEM … The End …