Find the Grid Cells that Contain Events

Description

Find the grid cells in a PolySet that contain events specified in EventData. Similar to findPolys, except this function requires a PolySet resulting from makeGrid. This restriction allows this function to calculate the result with greater efficiency.

Usage

findCells (events, polys)

Arguments

Details

The resulting data frame, a LocationSet, contains the columns EID, PID, SID (if in polys), and Bdry, where an event (EID) occurs in a polygon (PID, SID). The Boolean variable Bdry indicates whether an event lies on a polygon's edge. Note that if an event lies properly outside of all the polygons, then a record with (EID, PID, SID) does not occur in the output. It may happen, however, that an event occurs in multiple polygons (i.e., on two or more boundaries). Thus, the same EID can occur more than once in the output.

Value

LocationSet that links events with polygons.

See Also

combineEvents, findPolys, locateEvents, locatePolys, LocationSet, makeGrid.

Examples

#--- create some EventData: points in a diagonal line
events <- data.frame(EID=1:11, X=seq(0, 2, length=11),
                     Y=seq(0, 2, length=11))
events <- as.EventData(events, projection=1);
#--- create a PolySet (a grid)
polys <- makeGrid (x=seq(0, 2, by=0.50), y=seq(0, 2, by=0.50),
                   projection=1)
#--- show a picture
plotPolys(polys, xlim=range(polys$X)+c(-0.1, 0.1),
          ylim=range(polys$Y)+c(-0.1, 0.1), projection=1)
addPoints(events, col=2);
#--- run findCells and print the results
fc <- findCells(events, polys)
fc <- fc[order(fc$EID, fc$PID, fc$SID), ]
fc$label <- paste(fc$PID, fc$SID, sep=", ")
print (fc)
#--- add labels to the graph
addLabels(as.PolyData(fc[!duplicated(paste(fc$PID,fc$SID)), ],
                      projection=1),
          placement="CENTROID", polys=as.PolySet(polys, projection=1),
          col=4)