Geo Calculations

With Ruby

By Caleb Woods

Albers vs UTM

# Albers Equal Area Projection small_field = 35.85907491318873 acres large_field = 222.1015016221715 acres # UTM Zone 15 small_field = 35.87419394539743 acres large_field = 222.1926541039243 acres # Deltas small_field = 0.01511903220870181 acres large_field = 0.09115248175280044 acres

UTM Zones

A Polygon can span a UTM zone border

# Example of Polygon that spans UTM zones 15 and 16 # Calculated with Zone 15 304.64208165875334 acres # Calculated with Zone 16 304.64176688085104 acres # Split on Zone line and combined 304.6407631743717 acres For a ~300 acre field largest delta is 13 thousands of an acre

WKT Example

"MULTIPOLYGON (((-90.4738990305427 36.4133434167215, ... )))"

GeoJSON Example

{ "type": "Polygon", "coordinates": [ [ [-90.4738990305427,36.4133434167215], [-90.473979105792,36.4106894643104], [-90.4773486100253,36.4108323810396], [-90.4738853926222,36.4135819451996], [-90.4738990305427,36.4133434167215] ], [ [-90.4748795899079,36.4122608328937], [-90.4751238366577,36.4120176306662], [-90.4750501289294,36.4117390431922], [-90.4746434744808,36.4118880581738], [-90.4746528723027,36.4123276807651], [-90.4748795899079,36.4122608328937] ] ] }

GeoJSON Example

Questions?

Get the Slides

http://calebwoods.github.com/geocalculation