Query by clicking on a map

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Description

Click on a map (plot) to get values of a Raster* or Spatial* object at that location; and optionally the coordinates and cell number of the location. For SpatialLines and SpatialPoints you need to click twice (draw a box).

Usage

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## S4 method for signature 'Raster'
click(x, n=Inf, id=FALSE, xy=FALSE, cell=FALSE, type="n", show=TRUE, ...)

## S4 method for signature 'SpatialGrid'
click(x, n=1, id=FALSE, xy=FALSE, cell=FALSE, type="n", ...)

## S4 method for signature 'SpatialPolygons'
click(x, n=1, id=FALSE, xy=FALSE, type="n", ...)

## S4 method for signature 'SpatialLines'
click(x, ...)

## S4 method for signature 'SpatialPoints'
click(x, ...)

Arguments

x

Raster*, or Spatial* object (or missing)

n

number of clicks on the map

id

Logical. If TRUE, a numeric ID is shown on the map that corresponds to the row number of the output

xy

Logical. If TRUE, xy coordinates are included in the output

cell

Logical. If TRUE, cell numbers are included in the output

type

One of "n", "p", "l" or "o". If "p" or "o" the points are plotted; if "l" or "o" they are joined by lines. See ?locator

show

logical. Print the values after each click?

...

additional graphics parameters used if type != "n" for plotting the locations. See ?locator

Value

The value(s) of x at the point(s) clicked on (or touched by the box drawn).

Note

The plot only provides the coordinates for a spatial query, the values are read from the Raster* or Spatial* object that is passed as an argument. Thus you can extract values from an object that has not been plotted, as long as it spatialy overlaps with with the extent of the plot.

Unless the process is terminated prematurely values at at most n positions are determined. The identification process can be terminated by clicking the second mouse button and selecting 'Stop' from the menu, or from the 'Stop' menu on the graphics window.

See Also

select, drawExtent

Examples

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 r <- raster(system.file("external/test.grd", package="raster"))
#plot(r)
#click(r)
#now click on the plot (map)

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