locatePolys function

Locate Polygons on the Current Plot

Locate polygons on the current plot (using the locator

function).

locatePolys (pdata, n = 512, type = "o", ...)

Arguments

• pdata: PolyData (optional) with columns PID and SID (optional), with two more optional columns n and type.
• n: maximum number of points to locate.
• type: one of "n", "p", "l", or "o". If "p" or "o", then the points are plotted; if "l" or "o", then the points are joined by lines.
• ...: additional par parameters for the locator function.

Details

This function allows its user to define polygons with mouse clicks on the current plot via the locator function. The arguments n and type are the usual parameters for the locator function, but the user can specify them for each individual (PID, SID) in a pdata object.

If a pdata object exists, the function ignores columns other than PID, SID, n, and type. If pdata

includes n, then an outer boundary has n > 0 and an inner boundary has n < 0.

On exit from locator, suppose the user defined m

vertices for a given polygon. For that polygon, the X and Y columns will contain NAs where POS = (m+1):n for outer-boundaries and POS = (|n|-m):1 for inner-boundaries. The na.omit function can remove rows with NAs.

If a pdata object does not exist, the output contains only one polygon with a PID equal to 1. One inner-boundary polygon (POS goes from n to 1) can be generated by supplying a negative n.

If type = "o" or type = "l", the function draws a line connecting the last and first vertices.

Returns

PolySet with projection attribute equal to the map's projection. The function does not set the zone attribute.

Author(s)

Nicholas M. Boers, Staff Software Engineer

Jobber, Edmonton AB

Last modified Rd: 2007-06-06

See Also

addPolys, appendPolys, clipPolys, closePolys, findCells, findPolys, fixPOS, joinPolys, plotMap, plotPolys, thickenPolys, thinPolys.

Examples

#--- define one polygon with up to 5 vertices on the current plot
## Not run: polys <- locatePolys(n = 5)