epm (version 1.1.5)

interactiveExtent: Interactively choose extent

Description

Given a list of polygons or point occurrences, sets up an interactive plot to allow the user to draw the desired extent. This can be used to define the extent in createEPMgrid.

Usage

interactiveExtent(polyList, cellType = "square", bb = NULL)

Value

A list with a polygon, and its WKT string

Arguments

polyList

a list of Simple Feature polygons or points.

cellType

either hexagon or square.

bb

c(xmin, xmax, ymin, ymax) to limit the extent for the interactive plot.

Author

Pascal Title

Details

This function returns both a sf polygon and the same polygon as a WKT string. Either can be supplied to createEPMgrid as the extent. A recommended strategy is to use this function to find your extent, and to copy/paste the WKT string into your R script so that you can retain it for future use, and maintain reproducibility. See example.

What is chosen for cellType has no effect on what you might choose in createEPMgrid. Square cells will probably be fastest. If hexagons are selected, grid cell points are plotted instead of polygons to speed up plotting.

You may see the message Failed to compute min/max, no valid pixels found in sampling. (GDAL error 1) . This just means that a species did not register in any grid cells. This can be ignored.

The basemap is from https://www.naturalearthdata.com/.

Examples

if (interactive()) {
	ex <- interactiveExtent(tamiasPolyList)

	# You can use this as the extent in createEPMgrid
	grid <- createEPMgrid(tamiasPolyList, resolution = 50000, extent = ex$wkt)

	# One way to make your code reproducible would be to copy/paste the wkt 
	# in your code for future use:
	ex <- interactiveExtent(tamiasPolyList)
	ex$wkt
	customExtent <- "POLYGON ((-2238201 3532133, -2675450 1722657, -2470677 -317634, 
	-1863632 -1854074, -521614.8 -2170280, -349356.8 799040.9, -2238201 3532133))"

	grid <- createEPMgrid(tamiasPolyList, resolution = 50000, extent = customExtent)

}