Data compression Why compress (or ‘zip’)? Lossy vs. lossless For image archiving (satellite data) For image transfer over internet Lossy vs. lossless .jpeg is ‘lossy’ (some info. lost) .tiff is ‘lossless’ (no info. lost)

Data compression 281 kb 673 kb

Data compression 6.86 MB 15.2 MB

Data compression 6.2 MB 1.6 MB

Data compression Run-length codes Ex. # 1 Ex. # 2

Data compression Quadtree A quadtree recursively subdivides a plane into 4 quadrants If area is homogeneous, subdividing stops If the quadrant is heterogeneous with respect to this attribute, further subdivision occurs And so on, and so on, until…..

Data compression Quadtree

Data compression Quadtree 256 pixels down to to 80

Data compression Quadtree 2304 vs. 160 (or so); run on polygon, not line

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Lab Four GOAL: Make your .jpg of campus a georeferenced map layer that you can use in GIS software. Use your waypoints to NAIL the known coordinates to specific places on campus. Order: map, waypoint; map, waypoint;… INDEPENDENT WORK: Your group uses same Excel file