Queen's Aspect Ratio

Aspect roses for a floating point DEM on the left, and an integer version on the right.

Note the spikes on the integer version.  The Queen's aspect ratio calculates the severity of the spikes.

Diagonal := round(arctan(AverageYSpace/AverageXSpace) / DegToRad);  This compensates for geographic DEMs, where the 45 degree spikes might be at a different direction because 1 sec is not the same length in the x and y directions.

QueensAspect := (AspectFreq[0] + AspectFreq[Diagonal] + AspectFreq[90] +
AspectFreq[180-Diagonal] + AspectFreq[180] + AspectFreq[180+Diagonal] +
AspectFreq[270] + AspectFreq[360-Diagonal] + AspectFreq[360]) / (TotalAspects) * 45;

Low relief and short DEM spacing relative to the vertical resolution probably lead to larger values of the Queens aspect ratio.  DEM quality (partially expressed by the contour ghost ratio, probably not relevant to most current DEMs) probably also affects the ratio.

Floating point DEMs have ratios close to 1, and integer DEMs have a much larger ratio.

This was first introduced in MICRODEM 2001, with the work on the SSO diagram.

Last revision 12/11/2021