9/24/2014. Georeferencing: conclusions

Transcription

1 Georeferencing: conclusions 1

2 GEOG 300: UTM REVIEW QUIZ (0%) 1. The UTM system is composed of zones, each degrees longitude wide 2. The 0 value for northings is located at 3. The 0 value for eastings is located at ( a trick question) 4. What unit are eastings and northings coordinates measured in? 5. The maximum possible northings value in BC is approx? 6. In Canada, eastings have digits and northings have digits 2

3 Projection / Coordinate System has been defined: BC Albers Albers is an equal-area projection Projection / Coordinate System has been defined: UTM Transverse Mercator is a conformal (shape preserving) projection 3

4 Projection / Coordinate System has NOT been defined (but we can see its UTM) Projection / coordinate system undefined Review slides: georeferencing and projections Appendix A: Comparison of BC Albers and UTM The following identifies the maximum distortion for both BC Albers and UTM that was found when 1000-meter squares were constructed, and projected into each projection. UTM Distortions (within each UTM zone within BC) The maximum linear distortion is 0.040% The maximum area distortion is 0.08% BC Albers Distortions (within all of BC) The maximum linear distortion is 0.36% The maximum area distortion is 0.00% UTM preserves shape (distance) Albers preserves area Lab last week: one neighbourhood polygon measured in area: (?) UTM: sq km ( sq m) Albers: sq km ( sq m) Difference:.0218 sq km 21,800 sq m (= 0.08%) 4

5 Note: only UTM has zones -> Georeferencing: Rectification - imagery Georeferencing How do we make sure all our data layers line up? Georeferencing: = linking a layer or dataset with spatial coordinates Registration: = lining up layers with each other Rectification: The process by which the geometry of an image is made planimetric 5

6 Air photo: not georeferenced, registered or rectified Air photo rectified to match vector layer (roads), using Ground Control Points (GCPs) 6

7 Photos are not planimetric : there are distortions Tip, tilt and swing Relief distortion Radial distortion Photos (film now digital) are rectified and mosaiced to create Orthophotos [Ortho = upright or straight / overhead] 7

8 GIS Data creation Photogrammetry is the science of making measurements from photographs, especially for recovering the exact positions of surface points. Rectifying and registering air photos -> orthophotos 8

9 ORTHOPHOTOS Once corrected, and georeferenced, photos can be used for topographic mapping and as a mapping layer, with map data overlain on top. Aerial photograph Interpretation (API) Most of our base map GIS layers have come from air photos (BC- TRIM program) 9

10 Image interpretation GIS layer features are manually identified using: Shape Pattern Size Tone Colour Shadow Texture Site Time Provincial photography is redone only every years City photography more frequently: 3-5 years Smaller regions/countries would be flown more frequently PG

11 Digital photography 2000-> : rectification fast and automated GeoEye high resolution satellite image (50cm pixels) 2012 London Olympic stadium (satellite altitude: 700 km) Image layer included in GIS raster data for updating and checking Since 2000, the use of high resolution satellite imagery has increased 11

12 Google Earth- overlain georeferenced aerial photography and higher resolution satellite (ortho-) imagery; also including historical (ortho-)imagery Google Earth since 2005, using Landsat mosaic and global elevation model Myths about satellite imagery: The giant dog you can see from space Monday, June 9, 2008 BORIS the bull mastiff is so big that he can be seen lounging in his favourite position in the garden - from space. The 89kg dog has been captured on Google Earth's satellite images. His owners noticed an enormous brown blob on the image of their front garden and were stunned to discover it was their pet. 'He was in his favourite place,' said Fran Milner, from Bournemouth. We knew he was big but didn't think he was big enough to be seen from space. 12