PHOTOGRAMMETRIC MAP ACCURACY

HIGHWAY ENGINEERS USING LARGE-SCALE PHOTOGRAMMETRIC MAPPING FOR DETAILED DESIGN WORK REQUIRE CERTAIN STANDARDS OF HORIZONTAL AND VERTICAL ACCURACY FOR BOTH THE CONTROL SURVEYS AND THE MAPPING. VERTICAL ACCURACY OF MAPPING, AS REPRESENTED BY CONTOURS, IS THE MOST DIFFICULT TO ATTAIN AND IS GENERALLY THE GREATEST SOURCE OF TROUBLE. THE CALIFORNIA DIVISION OF HIGHWAYS IS MAKING A STATISTICAL ANALYSIS OF THE VERTICAL ACCURACY OF PHOTOGRAMMETRIC MAPPING OBTAINED UNDER CONTRACT. THE INFORMATION IS DERIVED FROM A COMPARISON OF FIELD ELEVATIONS WITH ELEVATIONS INTERPOLATED FROM CONTOUR MAPS. FIELD ELEVATIONS GENERALLY CONSIST OF A PROFILE OF THE FINAL LINE AS STAKED ON THE GROUND. THE DATA AS DEVELOPED FOR EACH PROJECT INCLUDE THE ARITHMETIC MEAN, STANDARD DEVIATION, CALCULATED C-FACTOR, AND A COMPARISON OF THE ERROR FREQUENCY DISTRIBUTION WITH THE THEORETICAL ERROR OR PROBABILITY CURVE. THE C-FACTOR IS CALCUATED FROM THE THEORETICAL CONTOUR INTERVAL WHICH WOULD COMPLY WITH THE 90 PERCENT SPECIFICATION REQUIREMENT AS DETERMINED FROM THE ERROR FREQUENCY DISTRIBUTION. ANALYSES HAVE BEEN COMPLETED ON SEVERAL PROJECTS MAPPED FOR 2-FT CONTOURS AT FLYING HEIGHTS OF FROM 1,500 TO 2,100 FT. RESULTS IN MOST CASES INDICATE CLOSE AGREEMENT BETWEEN THE ERROR FREQUENCY DISTRIBUTION AND THE THEORETICAL CURVE. THE CALCULATED STANDARD DEVIATIONS AGREE REMARKABLY WELL WITH THE 90 PERCENT SPREAD, INDICATING THE VALIDITY OF THE STATISTICAL APPROACH. IN TWO CASES VALUES OF THE ARITHMETIC MEAN INDICATE SYSTEMATIC ERRORS IN THE MAPPING. THE RESULTS SHOW THAT C-FACTORS OF 1,000 OR MORE SHOULD BE USED WITH EXTREME CAUTION IN PLANNING FOR 2-FT CONTOUR MAPPING, PARTICULARLY IF THE HORIZONTAL SHIFT IS NOT INCLUDED IN THE SPECIFICATIONS. STUDY OF THE DATA HAS LED TO INVESTIGATION OF THE MORE COMMON TYPES OF MAP ERRORS, THEIR DISTRIBUTION, PROBABLE CAUSE, AND METHODS OF PREVENTION. THE CHECKING AND INVESTIGATING OF PHOTOGRAMMETRIC MAPPING BY MEANS OF A KELSH PLOTTER HAVE ALSO DEVELOPED DATA ON SPOT HEIGHT ACCURACY ATTAINABLE UNDER CONTROLLED CONDITIONS WITH THIS INSTRUMENT. /AUTHOR/

Media Info

  • Monograph Title: Photogrammetry - developments and applications: 1958
  • Serial:

Subject/Index Terms

Filing Info

  • Accession Number: 00202709
  • Record Type: Publication
  • Files: TRIS, TRB
  • Created Date: Sep 16 1994 12:00AM