Analytical Adjustment Of Horizontal Aerotriangulation

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ROBERT E. ALTENHOFEN* U. S. Geological Survey kfenlo Park, Calif. Analytical Adjustment of Horizontal Aerotriangulation Versatility, economy, and increased accuracy have resulted from the numerical adjustment of blocks. (Abs/rac/ on next page) Il\TRODUCTION HE SY~TE~I ro~ ADJUSTMEKT of horizon tal used in the Pacific Area office of the Topographic Division, U. S. Geological Survey, employs the simplest algorithms to be found in published works on numerical photogrammetry. This office has an output of more than 400 7~-minute quadrangles per year, represen ting 22,000 sq uare miles of 1: 24,000-scale mapping. Continual change characterizes the system: numerical methods of adjustment will progress from the simple to more complex; horizontal aerotriangulation will expand to include the Z dimension; paper-tape output from a small computer ,,·ill gi,·e \I·ay to punched-card output from a large computer; addi tional stereoplotting instru men ts will increase the load on the readout equipment. OYerriding all \I·ill be the requiremen t to make changes with the least disruption to production. Smooth transition results if planning is thorough and the basic inpu ts to the systemnamely, aerial photographs and control identi fica tion-are properly processed. T aerotnangulatlOn and (3) the preparation of a planning diagram so necessary to good housekeeping. Figure 1 pictures the \\·ild PUG I point marker being used to make a stereoscopic transfer between diapositives from adjacent strips. A single drill hole (ha,·ing a diameter of 40 microns on ER-55 plates and 100 microns on contact plates) creates a pass point in each of the strips; thus each point is recorded monoscopically for use in su bseq uen t operations. Tf adjacent models are offset, two pass points per plate are transferred and marked opposite each fiducial mark in the center of the sidelap. Horizontal control points are identified in the field by paneling, either before or after aerial photography. About 10 per cent of the points are paneled before photography. The other 90 per cent are identified during field PllOCEDURE PLAKKING The planning operation includes: (1) the marking of pass points on diapositi,·es either in the reduced size for the ER-55 (B'alplex) stereoplotter or in full size for the Kelsh Autograph AS, and Stereoplanigraph C5; (2) the identification of horizontal control points on the aerial negativesor on the diapositives; * Presellted at the Annual Convention of the American Society of Photog~ammetry, \Vashington, ~. c., \1arch 1966. PublIcation authorized by the Director, U. . Geological Survey. 1047 ROBERT E. ALTENHOFEK 1048 PHOTOGRAMMETRIC ENGINEERING surveys, either by paneling the point or by substituting a well-defined image or "natural panel" for an ill-defined monumented point. However, there are few good geometric points in nature; therefore, natural images generally are not acceptable for controlling numerical aerotriangulation. All control points, whether or not paneled in advance of photography, are marked on the diapositives. Those points paneled during the survey operation are pho- 35-millimeter negative IS brought to the scale of the compilation negative by "zooming." The poin t is marked by filling the "dimple" with a grease pencil. Figure 3 is a print from a negative so marked. A planning diagram (Figure 4) serves to record all the point-marking operations. It carries a wealth of information, including (1) locations of numbered pass points; (2) locations of marked and numbered control points; ABSTRACT: Versatility, economy, and increased accuracy in horizontal block adjustment has resulted from the introduction of numerical photogrammetry. Semianalytical methods based upon rigorous transformations from high-order instrument coordinates to survey coordinates have a proper place beside the fully analytical methods. One such semianalytical system employed in the Pacific Area office, U. S. Geological Survey, involves the digitization of four different stereo plotting instruments, the ER-55 and Kelsh plotters, the Stereoplanigraph C5, and the Autograph A8. Data reduction includes transformation from model coordinates to strip coordinates, independent adjustment of strips to control when possible, and simultaneous second-degree conformal strip adjustment of the block. tographed from 3,000 feet above ground with a good 35-milli meter camera. When ER-55 diapositives are to be used, the control points are transferred from the 35-millimeter negatives to the compilation negatives, using a Zeiss snap marker and a zoom stereoscope. The marks are then carried to the diapositives in red uction printing. \iVhen con tact-size diapositives are to be used, the transfer is made directly to the diapositives with a PUG point marker. The lack of scale-equalization capability in the PUG is overcome by using film positives of the 35-millimeter exposures ratioed to diapositive scale. Figure 2 illustrates the snap-marker transfer operation; the FIG. 1. Using the PUG to transfer and mark pass points. (3) locations of marked miscellaneous points; (4) strip data required by the computer program; and (5) a record of progress. DATA DERIVATION The arrowheads in Figure 4 are affixed to the air-base segments of the flight lines to indicate the orientation of two- or threemodel sections. Successive section orientations differ by exactly 180 degrees, owing to the use of the "swing-around" method of scale and azimuth propagation along the FIG. 2. Transferring paneled horizontal control points from 35-millimeter negatives to the compilation negatives, obtained prior to paneling, using a snap marker and a zoom stereoscope. ANALYTICAL ADJUSTMENT OF HORIZONTAL .\EROTRI.\:-lGULATION 1049 FIG. 3. Transferred control point. the positive X axis to the right and is scaled by reference to ground control points, to a field-measured base, or to pass points from a previously scaled strip. After orientation of the section and readout of model coordinates, the cross le\'el is moun ted on the rightmost diapositive and the bubbles set to zero. The projector is rotated exactly 180 degrees so that the projected Y fiducial axis is parallel, after rotation, to its original direction. The strip. Figure 5 shows a three-projector Kelsh with a cross level resting on the diapositive of the left-hand projector. Figure 6 is a fourprojector ER-55 unit with cross level mounted on a platform above the left-hand projector. The "swing-around" procedure, used with eithet- instrument, allows a continuous strip buildup, section by section. Consider a strip to be scaled consisting of two-model Kelsh sections. The initial section of the strip has 2 I~ 2~40 ~I~ 2.\ [tILl a. ~145 I~ 120\ A C.Ot{TRoL !'T. o PA5,:>PoINT a Tl£ POINT 1050 l'HOTOGRAMMETRIC ENGINEERING FIG. 5. Three-projector Kebh plotter with cross-level. FIG. 6. Four-projector ER-55 plc,tter with cross-level. bubbles are releveled with the projector