Description Usage Arguments Details Value Author(s) See Also Examples

View source: R/distanceGridUnits.R

This function returns the distances in grid units between pairs of points on a square grid. This function is used in testing the accuracy of a calibration by comparing theoretical distances among grid points to measured distances.

1 | ```
distanceGridUnits(pairs, nx)
``` |

`pairs` |
a two-column matrix specifying the pairs of points between which the distance is to be found. |

`nx` |
the number of points in the first dimension along which grid points are counted (see "Details"). |

This function returns the distances in grid units between pairs of points on a square grid. Thus, adjoining points in the same row or column would be separated by a distance of one. The returned distances can then be multiplied by the grid square size to obtain the distances between pairs of points in real-world units (e.g. mm).

The input `pairs`

is a two-column matrix specifying the pairs of points, with the first column corresponding to one point and the second column to the other. The numbers in `pairs`

are indices of grid points (not point coordinates themselves). The assumed numbering scheme for the grid points is as follows: the points are first numbered across the first dimension (of length `nx`

) and then along a second dimension. For example, on a 5x4 grid points 1-5 would be across the first row, 6-10 across the second row, etc. For each row the point numbering starts in the same column. For `distanceGridUnits()`

the number of columns does not need to be specified since this can be found from the point index in `pairs`

. See "Examples" for an explanation of the numbering scheme.

a vector of the distances between the specified pairs of grid points.

Aaron Olsen

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 | ```
## INDICES OF POINT PAIRS ON A GRID WITH 5 ROWS
pairs <- matrix(c(1,1, 5,10, 6,16, 1,20), nrow=4, ncol=2, byrow=TRUE)
## FIND THE DISTANCE BETWEEN PAIRS OF POINTS IN GRID UNITS
## NOTE LAST DISTANCE IS 5 BECAUSE IT IS A 3,4,5-TRIANGLE
distanceGridUnits(pairs, nx=5)
## FOR ILLUSTRATION, HERE IS A GRID WITH 5 ROWS AND 4 COLUMNS
xy <- cbind(rep(0:4, 4), c(rep(0, 5), rep(1, 5), rep(2, 5), rep(3, 5)))
## PLOT THESE POINTS
plot(xy)
## PLOT LINE SEGMENTS CONNECTING THE PAIRS ABOVE
segments(x0=xy[pairs[, 1], 1], y0=xy[pairs[, 1], 2],
x1=xy[pairs[, 2], 1], y1=xy[pairs[, 2], 2],
col=c('blue', 'red', 'purple', 'green'))
``` |

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