Description Usage Arguments Details Value See Also Examples
Create a grid within the alpha hull of a set of points.
1 2 | build_grid_ahull_fill(coords, npts, pad = NULL, grid_opts = list(alpha
= 0.3, error_tol = 0.05, run_max = 20, verbose = FALSE))
|
coords |
A matrix or data.frame of coordinates with two columns |
npts |
The approximate number of points of the requested grid |
pad |
ignored argument |
grid_opts |
A list with component |
This function computes the alpha hull of a set of points, then
iteratively finds the best grid of npts
points fitting in the hull.
This function computes the alpha hull of a set of points which is
an estimate of its overall outline. The intricateness of this outline
is determined by the alpha
parameter: a value close to zero will
produce a very intricate outline and a high value will produce a coarse
outline (similar to the convex hull). It is highly recommended to try
different values of alpha
to see what is most appropriate for one's
datasets.
Parameter error_tol
controls the acceptable relative error in the
grid number of points (e.g. 0.1 for 10
control the iteration process.
The coordinates of a grid of points as a data.frame
with
approximately npts
rows and ncol(coords)
columns. Names
are transfered from the coords
data frame.
Other grid building functions: build_grid_ahull_crop
,
build_grid_identical
,
build_grid_squaretile
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 | data(meadow)
# Plot a grid with diagnostics
grid <- build_grid_ahull_fill(meadow[ ,c('lon','lat')], 10000,
grid_opts = list(verbose = TRUE))
plot(grid, pch = 21)
# See the influence of alpha parameter
par(mfrow = c(1, 4))
for ( alpha in c( .3, 1, 4, 10) ) {
grid <- build_grid_ahull_fill(meadow[ ,c('lon','lat')], 10000,
grid_opts = list(alpha = alpha))
plot(grid, pch = 21)
title(paste0("alpha=",alpha))
}
|
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