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Spatial Point Patterns
book

Spatial Point Patterns

by Adrian Baddeley, Ege Rubak, Rolf Turner
November 2015
Intermediate to advanced content levelIntermediate to advanced
828 pages
33h 11m
English
Chapman and Hall/CRC
Content preview from Spatial Point Patterns
Poisson Models 309
For example, atan calculates angles in radians; to convert them to degrees, we would need to
multiply by 18 0/
π
, so the covariate sho uld be atan(grad) * 180/pi. To prevent the mathemat-
ical symbols * a nd / from being interpreted a s model formula ope rators, this expression should be
enclosed inside the function I (fo r ‘ide ntity’):
> ppm(bei
~
I(atan(grad) * 180/pi), data=bei.extra)
The function I retur ns its argument unchanged, and the r ules for interpreting a formula ensure that
the expression inside the parentheses is evaluated using the usual mathematical operations. T he
command above fits a loglinear model dep ending on the a ngle o f inclination, expressed in degrees.
It may be neater to write a separate R function which ...
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Publisher Resources

ISBN: 9781482210217