GISTools (version 0.7-4)

Add masking around an image: Draw a mask around a Grid Based Image

Description

Takes an `mask' type polygon object - basically a rectangle with a polygon hole cut through it - and draws this over an image. This has the effect of only showing the image inside the hole. This is useful for plotting surfaces defined over a study area, but masking the values outside of the area.

Usage

add.masking(maskPoly,color)

Arguments

maskPoly

A masking polygon as described above.

color

Colour of the mask. Defaults to white, but for example, sea could be shown as blue.

Value

Details

Returns no value, but draws a mask on the current graphics device as a side effect

See Also

poly.outer, kde.points.

Examples

# Data for New Haven to use in example
data(newhaven)
# Do the KDE
breach.dens = kde.points(breach,lims=tracts)
# Plot the result
level.plot(breach.dens)
# Block out the part outside the study area
masker = poly.outer(breach.dens,tracts,extend=100); add.masking(masker)
# Plot census tract boundaries
plot(tracts,add=TRUE)