get_flightline_info: Get summary information for flight line extents

In mbedward/CERMBlidar: A collection of functions to process aerial LIDAR data

Get summary information for flight line extents

Description

This function determines the minimum bounding rectangle for points in each flight line and, based on this, the orientation of the flight line: one of 'NS' (north - south), 'EW' (east - west), or XX (indeterminate). Note: this function pre-dates the similar function get_flightline_polygons and the two might be merged in a future version of the package.

Usage

get_flightline_info(las, angular.tol = 25, min.ratio = 1.2, min.points = 1000)

Arguments

las	A LAS object, e.g. imported using prepare_tile.
angular.tol	The angular tolerance in degrees to apply when determining flight line orientation. It refers to the angle between the longest side of bounding rectangle and the horizontal (X coordinate axis). The default value is 25 degrees and the valid range of values is 0 < angular.tol <= 30.
min.ratio	The minimum ratio (default = 1.2) of the longest to the shortest side of a flight line bounding rectangle for orientation to be either 'NS' or 'EW'. Must be a value greater than 1.1. For flight lines with more equilateral bounding rectangles, orientation is determined by examining point GPS times (see Details).
min.points	The minimum number of points in a flight line for it to be included. Set to zero to include all flightlines. The default value (1000) is intended to exclude flight lines that only appear at the margins of the tile. Normally, such sparse flight lines will be removed when importing the tile. In the case that all flight lines are included, bounding rectangles and orientations will not be defined for those with very few points.

Details

To determine orientation, the function first checks the angle between the longest side of the rectangle and the horizontal (X coordinate axis). If the longest side is close to horizontal (where 'close' means plus or minus a tolerance value specified with the angular.tol argument which has a default value of 30 degrees) the orientation is provisionally labelled as 'EW', whereas if the longest side is close to vertical (Y coordinate axis) it is provisionally labelled as 'NS'. Flight lines that are not sufficiently close to horizontal or vertical are labelled as 'XX' and not considered further.

For flight lines labelled 'NS' or 'EW', if the ratio of the longest side of the bounding rectangle to the shortest side is greater than that specified by the ratio.side argument (default 1.2), the initial orientation is taken as confirmed. For flight lines with more equilateral bounding rectangles, the point GPS times are checked along the X and Y dimensions to determine the final orientation.

Value

A spatial data frame (class sf) with columns: flightlineID, xlen, ylen, orientation and geometry (minimum bounding rectangle of flight line).

See Also

check_flightline_orientation

mbedward/CERMBlidar documentation built on April 10, 2024, 2:05 p.m.