`gzAzimuth.Rd`

The function finds azimuth values for geographical coordinates given as decimal degrees from the `from`

coordinates to the `to`

coordinate. In function `trackAzimuth`

, the azimuth values are found between successive rows of the input coordinate matrix.

gzAzimuth(from, to, type = "snyder_sphere") trackAzimuth(track, type="snyder_sphere")

from | a two column matrix of geographical coordinates given as decimal degrees (longitude first) |
---|---|

track | a two column matrix of geographical coordinates given as decimal degrees (longitude first) |

to | a one row, two column matrix or two element vector of geographical coordinates given as decimal degrees (longitude first) |

type | default is |

The azimuth is calculated on the sphere, using the formulae given by Snyder (1987, p. 30) and Abdali (1997, p. 17). The examples use data taken from Abdali (p. 17--18). There is a very interesting discussion of the centrality of azimuth-finding in the development of mathematics and mathematical geography in Abdali's paper. Among others, al-Khwarizmi was an important contributor. As Abdali puts it, "This is a veritable who's who of medieval science" (p. 3).

values in decimal degrees - zero is North - of the azimuth from the `from`

coordinates to the `to`

coordinate.

Snyder JP (1987) Map projections - a working manual, USGS Professional Paper 1395; Abdali SK (1997) "The Correct Qibla", formerly at http://patriot.net/users/abdali/ftp/qibla.pdf

Roger Bivand, with contributions by Sebastian Luque

name <- c("Mecca", "Anchorage", "Washington") long <- c(39.823333, -149.883333, -77.0166667) lat <- c(21.423333, 61.2166667, 38.9) x <- cbind(long, lat) row.names(x) <- name crib <- c(-9.098363, 56.575960) r1 <- gzAzimuth(x[2:3,], x[1,]) r1#> Anchorage Washington #> -9.098363 56.575961#> [1] "names for target but not for current"r2 <- gzAzimuth(x[2:3,], x[1,], type="abdali") r2#> Anchorage Washington #> -9.098363 56.575961#> [1] "names for target but not for current"trackAzimuth(x)#> [1] 4.691489 82.234220