A new tool has been developed for OzTrack by Dr Ross Dwyer (OzTrack Scientific Data Analyst) which enables users with telemetry data collected from the Pacific region to accurately assess animal movement and home range use.
The International Date Line (IDL) runs from the North Pole to the South Pole passing through the middle of the Pacific Ocean roughly following 180° west (-180° longitude) and 180° east (+180° longitude) of the Prime Meridian.
In previous versions of OzTrack, home range calculations from tagged animals crossing the IDL would return erroneous values as the polygon stretched west to east across the Indian and Atlantic Oceans rather than passing across the IDL.
Rather than crossing the International Date Line, the Minimum Convex Polygon (MCP) calculated from the the seabird geolocator locations crosses the prime meridian generating extremely large estimates of range use.
This new feature (soon to be implemented into the website oztrack.org) handles these objects by splitting the polygon down the 180th meridian, effectively forming two independent polygons to the east and to the west of the IDL.
This ensures all area calculations are accurate when the polygons are projected into the relevant coordinate system and that the mapping of polygons within OzTrack and Google Earth appear as expected.
Using the new tool, the Minimum Convex Polygon (MCP) generated from the geolocator data now crosses the International Date Line
Filed under: Uncategorized Tagged: 180th meridian, analysis tools, international date line, OzTrack, Prime meridian, Ross Dwyer
