make_transects: Make transect lines for sampling

In paulhegedus/SampleBuilder: Functions for building sampling designs

Make transect lines for sampling

Description

For returning a specified number of transects perpendicular to a user supplied line feature. User options include the number of transects, the length of the transect (in meters), and the size (assumed to be a square) of each transect cell (in meters).

Set 'buddy_t' to TRUE to generate a transect less 3 transect sizes away but at least 1 transect size away so that sampling can be performed traveling away from the line feature and back to the line feature.

The direction specifies which direction from the line layer transects should be generated. Typically "positive" indicates transects to the North and West while "negative" generates transects to the South and East. Default is both directions from the line layer. Recommended to play with and decide for your needs.

While all overlaps are not guaranteed to be removed, setting 'allow_overlaps' to FALSE (default) will restrict sampling to where the risk is minimized. This is done by making a buffer the width of the transects around the line layer and removing sections of the line layer where the buffer overlaps.

Note, if the number of transects are smaller than the number of distinct line features then transects will be placed on random line features. If the number of transects is equal to the number of distinct line features then one transect will be placed on each line feature. If the number of transects is greater than the number of line features then at least one transect will be placed on each line feature and remaining transects will be distributed by the length of line features (e.g. longer line features have more transects).

Usage

make_transects(
  line_layer_path,
  poly_layer_path = NULL,
  poly_strat_col = NULL,
  t_number,
  t_length,
  t_size,
  buddy_t = TRUE,
  direction = c("positive", "negative"),
  allow_overlaps = FALSE
)

Arguments

line_layer_path	Character, path to the .shp file of the line layer to build transects from.
poly_layer_path	Optional character, path to the .shp file of the polygon layer to stratify transects on.
poly_strat_col	TODO - Optional character, column name to use for stratifying.
t_number	Numeric, the approximate number of transects to generate.
t_length	Numeric, the desired length of transects (in meters).
t_size	Numeric, the size (Y x Y) of the transect cells (in meters).
buddy_t	Logical, default is TRUE, whether to include a buddy transect for efficient sampling.
direction	Character, default is c("positive", "negative"), the direction from the line layer transects should be built.
allow_overlaps	Logical, default is FALSE, whether to remove areas of line where transects could overlap with other transects.

Value

A 'sf' object with transect lines and ID numbers in lat long.

paulhegedus/SampleBuilder documentation built on July 21, 2023, 9:35 a.m.