Locate polygons on the current plot (using the locator
function).
locatePolys (pdata, n = 512, type = "o", ...)PolySet with projection attribute equal to the map's
projection. The function does not set the zone attribute.
PolyData (optional) with
columns PID and SID (optional), with two more
optional columns n and type.
maximum number of points to locate.
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.
Nicholas M. Boers, Staff Software Engineer
Jobber, Edmonton AB
Last modified Rd: 2007-06-06
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.
addPolys,
appendPolys,
clipPolys,
closePolys,
findCells,
findPolys,
fixPOS,
joinPolys,
plotMap,
plotPolys,
thickenPolys,
thinPolys.
#--- define one polygon with up to 5 vertices on the current plot
if (FALSE) polys <- locatePolys(n = 5)
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