The elliptical dimensions output grid themes give the a, b, and c dimensions for a simple ellipse as shown below. The methods are described in Finney (1998).
The units of the elliptical dimensions are rates of spread displayed as meters per minute (m/min), feet per minute (ft/min), or chains per hour (chains/hr).
The elliptical dimensions can be used to calculate rates of spread in other than the maximum direction. Future features in FlamMap will also utilize elliptical dimensions.