distanceToPoint {celltrackR}

Distance to a Reference Point

Description

Compute the distance between the starting point of a track and a reference point. Useful to detect directed movement towards a point (see examples).

Usage

distanceToPoint(x, p = c(0, 0, 0), from = 1)

Arguments

x

a single input track; a matrix whose first column is time and whose remaining columns are a spatial coordinate.

p

numeric vector of coordinates of the reference point p to compute distances to.

from

index, or vector of indices, of the first row of the track. If from is a vector, distances are returned for all steps starting at the indices in from.

Value

A single distance.

See Also

angleToPoint to compute the angle to the reference point, and AngleAnalysis for other methods to compute angles and distances.

Examples

## Plotting the angle versus the distance to a reference point can be informative to
## detect biased movement towards that point. We should be suspicious especially
## when small angles are more frequent at lower distances.
steps <- subtracks( Neutrophils, 1 )
bb <- boundingBox( Neutrophils )
angles <- sapply( steps, angleToPoint, p = bb["max",-1] )
distances <- sapply( steps, distanceToPoint, p = bb["max",-1] )
scatter.smooth( distances, angles )
abline( h = 90, col = "red" )