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Testing the Vertical Positional Accuracy of Digital Elevation Data

Testing the Vertical Positional Accuracy of Digital Elevation Data. Indiana GIS Conference February 18, 2009 Robert W. (Bob) Wilkinson Indiana DNR, Division of Water. Why Test for Vertical Accuracy. Does the data meet contract specifications?. Does the data meet your needs?.

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Testing the Vertical Positional Accuracy of Digital Elevation Data

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  1. Testing the Vertical Positional Accuracy of Digital Elevation Data Indiana GIS ConferenceFebruary 18, 2009 Robert W. (Bob) Wilkinson Indiana DNR, Division of Water

  2. Why Test for Vertical Accuracy • Does the data meet contract specifications? • Does the data meet your needs?

  3. What About Horizontal Accuracy? The Only Deliverable in Our 2008 Mapping Was a Digital Terrain Model. Past mapping experience has shown that photogrammetric mapping with good vertical accuracy will have good horizontal accuracy.

  4. Office Review Looking for Problems Along Roads Horizontal Accuracy

  5. Which Standard to Use?National Map Accuracy Standards (NMAS)National Standard for Spatial Data Accuracy (NSSDA)

  6. National Map Accuracy StandardsLast Revised in 194790% of Test Points Within ½ Contour Interval.What About the Other 10%?Does the Map Meet the Standard? (Pass/fail)

  7. National Map Accuracy StandardsUsed by DNR 1965 - 1998

  8. National Map Accuracy StandardsUsed by DNR 1965 - 1998

  9. National Standard for Spatial Data AccuracyIssued by FGDC in 1998 http://www.fgdc.gov/standards/projects/FGDC-standards-projects/accuracy/part3/chapter3

  10. National Standard for Spatial Data Accuracy Objective The National Standard for Spatial Data Accuracy (NSSDA) implements a statistical and testing methodology for estimating the positional accuracy of points on maps and in digital geospatial data, with respect to georeferenced ground positions of higher accuracy.

  11. National Standard for Spatial Data Accuracy Accuracy Testing by an Independent Source of Higher Accuracy Is the Preferred Test for Positional Accuracy.

  12. National Standard for Spatial Data Accuracy The independent source of higher accuracy shall be of the highest accuracy feasible and practicable to evaluate the accuracy of the dataset.

  13. National Standard for Spatial Data Accuracy The independent source of higher accuracy shall be acquired separately from data used in the aerotriangulation solution or other production procedures.

  14. Independent Source of Higher Accuracy Another Map

  15. Bench Marks from NGS

  16. Bench Marks from DNR

  17. National Standard for Spatial Data Accuracy 95% Confidence Level defined as 1.960 * RMSEz Reporting: °Tested ___ Feet at 95% Confidence °Compiled to meet ___ Feet at 95% Confidence

  18. Check Point Locations Check points may be distributed more densely in the vicinity of important features and more sparsely in areas that are of little or no interest.

  19. Check Point Locations For a dataset covering a rectangular area that is believed to have uniform positional accuracy, check points may be distributed so that points are spaced at intervals of at least 10 percent of the diagonal distance across the dataset and at least 20 percent of the points are located in each quadrant of the dataset.

  20. National Standard for Spatial Data Accuracy If fewer than twenty points can be identified for testing, use an alternative means to evaluate the accuracy of the dataset. SDTS identifies these alternative methods for determining positional accuracy: °Deductive Estimate °Internal Evidence °Comparison to Source

  21. 2008 Division of Water Location of 12 ProjectsAlso Included Bridge Surveys

  22. Total Station

  23. Beehunter Ditch at Linton

  24. Sewage Plant BridgeBeehunter Ditch at Linton

  25. Sewage Plant Bridge

  26. Bridge Section Points

  27. Edited Points for Map Check

  28. Surface Spot From ArcToolbox

  29. Surface Spot From ArcToolbox

  30. Table Before Surface Spot

  31. Table After Surface Spot

  32. Add and Calculate a New Field

  33. Check Statistics

  34. Import Table Into Excel

  35. Re-check Mean, Max, and Min An average that is not close to zero may indicate a systematic error.

  36. Square the Errors

  37. Calculate RMSEz and NSSDA 95% Confidence Level Contract called for 1.2 foot accuracy at 95% Confidence. Map is Good

  38. Accuracy Checks With Simple Equipment

  39. Accuracy Checks With Simple Equipment

  40. Accuracy Checks With Simple Equipment

  41. Accuracy Checks With Simple Equipment

  42. Windy Hill Subdivision in Greencastle

  43. Windy Hill Subdivision in Greencastle

  44. Windy Hill Subdivision in Greencastle

  45. Windy Hill Subdivision in Greencastle

  46. Windy Hill Subdivision in Greencastle

  47. Windy Hill Subdivision in Greencastle

  48. Check Level Notes in Excel and Join Tables

  49. Use Surface Spot Command and Excel as Before

  50. Edinburgh East Side Swale

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