1. Surveying and Digitizing

2. Primary Data Sources Measurements Field → surveying Lab (not covered here) Remotely sensed data already secondary? Creating geometries Definitely in the realm of secondary data Digitizing Scanning

3. Surveying Measurements and measurement techniques Distances Angles Position determination Applications Traversing and mapping Construction and earthwork Boundary surveys

4. Definition of Surveying General To inspect, view, scrutinize, or examine To determine condition, situation, or value Specifically Science and art of determining relative positions of points above, on, or beneath earth surface

5. Uses of Surveying Locate/map resources Engineering design Layout construction or engineering projects Verify performance Acquire reliable data Provide control Usually for location

6. History of Surveying Early applications Boundary location Construction Mapping Early surveys limited by technology Crude and inconsistent methods Development of sighting devices, standards, …

7. History of Surveying (2) Industrial revolution improved surveying Advances in available materials Improvement in tools Electronics revolution  fundamental advances Electronic distance and angle measurement Satellite surveying Enhanced processing

8. Specific Types of Surveying Property (cadastral) surveying Control surveying Mapping surveying (planimetric or topographic) Photogrammetric surveying Construction (engineering) surveying Route surveying Hydrographic surveying

9. Surveying Measurements Two quantities measured in surveying Lengths Angles All measurements are imperfect Errors Mistakes

10. Measurement Errors Sources of errors Natural Instrumental Types of errors Systematic Random Terms used in describing errors Precision Accuracy Personal

11. Idea of Relative Position Question: Have the points moved? Answer: Relative to what? References Needed for expressing location of points, lines, other objects Datums provide references in surveying Horizontally Vertically

12. Reference Ellipsoids Basic Concept b = semi-minor axis f = flattening a = semi-major axis e = eccentricity

13. Example Reference Ellipsoids EllipsoidEquatorial AxisPolar AxisAssociation Clarke, 186612,756,412.8 m12,713,167.6 mNAD27 datum GRS8012,756,274 m12,713,504.6 mNAD83 datum WGS8412,756,274 m12,713,504.6 mGPS ITRS12,756,272.98 m12,713,503.5 mITRF GRS= Geodetic Reference System WGS= World Geodetic System ITRS= International Terrestrial Reference System

14. Ignoring Earth Curvature 8000.000m (  5 miles) 8000 (  5 + 0.25”).006m miles  998.95 km 1000 km Distance

15. Ignoring Earth Curvature (2) 1 mile (1609 m) 8 inches (  20 cm) Level surface Horizontal plane Level line

16. Ignoring Earth Curvature (3) 75 mi 2 (48,000 acres) 19,800 hectares Sum of Interior Angles = 180° 00' 01" Triangle geometry

17. Digitizing and Scanning Instruments Georeferencing The process and problems associated with it Automation Formats

18. Why Do We Have To Digitize? Existing data sets are general purpose, so if you want something specific you have to create it In spite of 20+ years of GIS, most stuff is still in analog form Chances are somebody else has digitized it before; but data sharing is not what it should be

19. Digitizer Digitizing table 10” x 10” to 80” x 60” $50 - $2,000 1/100 th inch accuracy Stylus or puck with control buttons

20. The Digitizing Procedure Affixing the map to the digitizer Registering the map Actual digitizing In point mode In stream mode

21. Georeferencing at least 3 control points aka reference points or tics easily identifiable on the map exact coordinates need to be known

22. Digitizing Modes Point mode most common selective choice of points digitized requires judgment for man-made features Stream mode large number of (redundant) points requires concentration For natural (irregular) features

23. Problems With Digitizing Paper instability Humidity-induced shrinking of 2%-3% Cartographic distortion, aka displacement Overshoots, gaps, and spikes Curve sampling

24. Errors From Digitizing Fatigue Map complexity ½ hour to 3 days for a single map sheet Sliver polygons Wrongly placed labels

25. Digitizing Costs Rule of thumb: one boundary per minute ergo: appr. 62 lines = more than one hour

26. Automated Data Input (Scanning) Work like a photocopier or fax machine Three types: Flatbed scanners A4 or A3 600 to 2400 dpi optical resolution $50 to $2,000 Drum scanner practically unlimited paper size $10k TO $50k Video line scanner produces vector data

27. Requirements for Scanning Data capture is fast but preparation is tedious Computers cannot distinguish smudges Lines should be at least 0.1 of a mm wide Text and preferably color separation AI techniques don ’ t work (yet?) Symbols such as  are too variable for automatic detection and interpretation

28. Semi-automatic Data Input (Heads-up Digitizing) Reasonable compromise between traditional digitizing and scanning Much less tedious Incorporating your intelligence

29. Criteria for Choosing Input Mode Images without easily detectable line work should be left in raster format Really dense line work should be left as background image – unless it is really needed for automatic GIS analysis; in which case you would have to bite the bullet

30. Conversion from Other Databases Autocad.dxf and dBASE.dbf are de facto standards for GIS data exchange In the raster domain there is no equivalent;.tif comes closest to a “standard” In any case: merging data that originate from different scales is problematic – in the best of all worlds; there is no automatic generalization routine