Adjust for Edge Effects
Shrink a point pattern, or expand it through replication.
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A spatstat point pattern object (class
Distance from the edges to shrink, if negative, or to expand, if positive.
Distance from the edges.
When computing assimilation or competition indices, those near the edges of the study region are distorted because the outside is empty. Common solutions to this problem are not to use indices computed for plants near the edges, or (with rectangular regions) to attach translated copies, thus changing the topology into a torus. This function implements both strategies. When expanding, the part of the copies to be used can be specified to avoid unnecessary computation.
Typically, in the first case the indices are computed for the full pattern, and then the edges are discarded using
edges with a negative
width. In the second case, the point pattern is first expanded with
edges(plants, width), the indices are computed for the expanded pattern, and then the result is restricted to the original size with
core returns a logical vector indicating which plants are at more than the given distance from the edges. With a negative
edges(plants, width) is the same as
edges returns a point pattern with the same structure as
width is negative, the parts of the pattern that are at a distance less than
-width from an edge are discarded.
width is positive, the pattern is first expanded by surrounding it with 8 shifted copies (the window must be rectangular). Then, the parts of the pattern that are at a distance less than
width from an edge of the enlarged pattern are discarded.
width = 0,
plants is returned unchanged.
core returns a logical vector with
TRUE for the plants that are at more than the given distance from the edges, and
Requires the spatstat package.
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