viewshed3d: Tools to compute visibility in 3D point clouds of ecosystems

In Blecigne/viewshed3d: Compute Viewshed in 3D Point Clouds of Ecosystems

Tools to compute visibility in 3D point clouds of ecosystems

Description

For many animals, the ability to visually assess the environment and detect approaching predators is an important part of anti-predator strategies. Because this can occur across spatial scales, estimation of the viewshed can help to quantify visibility as a continuous variable around animal locations and facilitate studies of habitat selection and predator-prey interactions.

Details

Visibility and cumulated viewsheds

visibility within a spherical viewshed is calculated using the visibility function. This function is designed to sample the point cloud in every direction of the 3D space from a single user-defined location and to record the distance to the nearest point in each direction. Each direction is thus considered as a sightline - of a user defined angle - that is assumed to end when an object is encountered. The d_visibility function (for directional visibility) provides similar capabilities than the visibility function but enable to segment the viewshed to analyse the visibility in a particular direction. The h_visibility function (for horizontal visibility) computes the visibility in a viewshed defined as a disk. This enable to compute the extend of animal visibility parallel to the ground. The viewsheds function computes the overlap between viewsheds calculated from different locations and returns a voxel cloud quantifying for each voxel (i.e. each portion of the 3D scene) the number of times it was visible from any location.

Ground reconstruction

in the point clouds, some portions of the ground is frequently not sampled by the sensor (especially in the case of a TLS). That would result in infinite sightlines that continue below the ground surface. To correct for this effect, the reconstruct_ground function can be used to reconstruct the ground before using the visibility function. The reconstruct_ground function computes the optimal resolution to reconstruct the ground based on user-defined parameters for visibility calculation.

3D scene reshaping

because 3D scenes might cover a large area, but the visibility analyses might be computed for smaller areas, the sample_scene function can be used at the beginning of the data preparation process to segment a scene, with the appropriate properties in terms of size and shape for visibility calculation. This might be usefull to reduce computation time during the ground reconstruction process.

Noise filters

the denoise_scene function provides three different methods to filter isolated points from 3D point clouds. The remove_slope function enable to remove the slope from a 3D scene and the add_slope function reverse this operation.

Other functions

the generate_sphere function can be used to generate a spherical point cloud with a user defined angular resolution. The set_position function computes the correct elevation for the animal position based on the ground elevation.

Dataset

the viewshed3d package provides a TLS scene of a circular forest plot located at northern treeline sites in Alaska (tree_line_plot.laz). This dataset has the following specifications :

• Format: LAS

• 2513044 points

• radius: 17 m

• center coordinates: 0,0,0

• duplicated points removed

• dowsampled by keeping one point within a 2 cm voxel

Blecigne/viewshed3d documentation built on Nov. 5, 2022, 9:08 p.m.