Standard Deviational Ellipse
Create a standard deviational ellipse for a set of points
A standard deviational ellipse is produced according to two methods, with variations. The default method is the on presented by Robert Yuill (1971). This method does not correct for degrees of freedom. The Yuill method does not give a radius equal to the standard distance deviation for a random point distribution (to achieve this, the SDs should be multiplied by sqrt(2), as explained in the CrimeStat documentation). The plugin also offers the CrimeStat / aspace method, where there are corrections for degrees of freedom and with sqrt(2). A polygon vector layer with the standard deviational ellipse is produced, containing the attributes: meanx, meany, majorsd, minorsd, majorangle, directoind and eccentrici as explained in the documentation. The majorangle is counter-clockwise relative to the first axis. An attribute for weighting can be selected. There are no external library dependencies.