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Point Radius Method

Point Radius Method. Uncertainty and Best Practices. Best Practices Resources. MaNIS/HerpNET/ORNIS Georeferencing Guidelines http://manisnet.org/GeorefGuide.html Guide to Best Practices in Georeferencing http://www.gbif.org/participation/training/resources/gbif-training-manuals

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Point Radius Method

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  1. Point Radius Method Uncertainty and Best Practices

  2. Best Practices Resources MaNIS/HerpNET/ORNIS Georeferencing Guidelines http://manisnet.org/GeorefGuide.html Guide to Best Practices in Georeferencing http://www.gbif.org/participation/training/resources/gbif-training-manuals (http://www.gbif.org/orc/?doc_id=1288h)

  3. Scale Uncertainty (ft) Uncertainty (m) 1:1,200 3.3 ft 1.0 m 1:2,400 6.7 ft 2.0 m 1:4,800 13.3 ft  4.1 m 1:10,000 27.8 ft 8.5 m 1:12,000 33.3 ft 10.2 m 1:24,000 40.0 ft  12.2 m 1:25,000 41.8 ft 12.8 m 1:63,360 106 ft 32.2 m  1:100,000 167 ft 50.9 m 1:250,000 417 ft 127 m Sources of uncertainty: 20° 30’ N 112° 36’ W • Coordinate Uncertainty • Map scale • The extent of the locality • GPS accuracy • Unknown datum • Imprecision in direction measurements • Imprecision in distance measurements (1km vs. 1.1km)

  4. Determining uncertainties • Precision vs. accuracy • Extent of locality • GPS accuracy • Unknown datum • Imprecision in distance measurements • Imprecision in coordinate measurements • Map scale • Imprecision of direction measurements

  5. Less Precise More Precise Precision vs. AccuracyDisambiguated Precision is… …the level of detail contained in or described by the data. Example: 42, precise 42.1, more precise 42.01, even more precise Precision can help to minimize uncertainty.

  6. x More Accurate Less Accurate Precision vs. AccuracyDisambiguated Accuracy is… …a measure of how close a given value is to the true value.* Example: Truth = 42 41.999 = more precise, less accurate *We may never actually know the true value in georeferencing, but we do our best to reproduce the location of the true location.

  7. Precision vs. AccuracyDisambiguated Final Answer? The sum of what we know… about what we don’t know… is the uncertainty.

  8. The Extent of the Locality

  9. The Extent of the Locality over Time Yellow polygon from GEOLocate

  10. GPS Accuracy 5m 9m

  11. Unknown Datum Error assuming NAD27 vs. NAD83 or WGS84

  12. Imprecision in Distance Measurements

  13. Imprecision in Coordinate Measurements Uncertainty based on coordinate precision using the WGS84 reference ellipsoid 20° 30’ N 112° 36’ W vs. 20° 30’ N 112° 30’ W

  14. Map Scale 1/30th (.033) inch 1/50th (.02) inch USGS Map Accuracy USGS Standard: "For maps on publication scales larger than 1:20,000, not more than 10 percent of the points tested shall be in error by more than 1/30 inch, measured on the publication scale; for maps on publication scales of 1:20,000 or smaller, 1/50 inch."

  15. Imprecision of Direction Measurements Error: N > NE > ENE

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