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This is effectively a ‘wrap-around’ version of the normal line-plot. It can be used for data which is intrinsically directional (such as frequency of wind directions) or to compare several items on multiple categories.
ch.Polar values
Examples
Here is an example from the Proceedings of the Yorkshire Geological Society showing how fossil corals were aligned to the prevailing current directions [PYGS 52.4 p.358]:
ch.Set'boxed,nomarkers,surface'
ch.Set('head' 'Coral;alignments;at Greenfield')('Hstyle' 'Left')
ch.Set('ystyle' 'grid,forcezero')('vm' 8)('pattern' 4)
ch.Set('xstyle' 'grid')('yr' 0 25) © 30 degree radii
ch.Polar 10 15 15 25 15 25 10 15 15 25 15 25
PG„ch.Close
In this example, you can omit the X-tick setting as the default is to make tick marks at each data point. An example which compares two (imaginary) cars on 7 criteria shows this:
ch.Set'boxed,forcezero,grid'
ch.Set('head' 'Cars;compared')('Hstyle' 'Left')('vm' 8)
ch.Set'xlab' 'Speed,Fuel,Comfort,Reliability,Safety,Seating,Service interval'
ch.Set('Key' 'Volvo' 'Saab')
ch.Polar 18+?7 2½24
PG„ch.Close
Finally, you can use the ‘risers’ style to join each point to the centre. If you omit the lines and use arrowheads and risers, this works very well as a simple radial frequency plot:
ch.Set'boxed,nolines,risers,arrows,forcezero'
ch.Set('head' 'Frequency of;wind direction;in Gilling')('Hstyle' 'Left')
ch.Set('nib' 0.8)('vm' 4)('ystyle' 'noax')('xstyle' 'noax')('astyle' 6 30)
ch.Polar 4+?8½9
PG„ch.Close
All the normal axis and style settings apply as you would expect. If you use the ‘surface’ style with cumulative values, you will need to be careful to draw the outer data first. Note that the X-labels are always written radially around the circumference. You cannot use the ‘Intercept’ property here to move the axis positions – the Y-axis is always drawn to the 12-o’clock position, and the X-axis is always drawn around the outside. You may use the ‘background’ colour to fill the circle edged by the X-axis.
See also ...
Polarchart Style