A convenience wrapper around PROJ::proj_trans() for converting
projected coordinates to geographic. Useful for generating regular grids
in a projected CRS to feed to tissot(), which requires lon/lat input.
Arguments
- x
input coordinates — any xy-ish object: a two-column matrix, data.frame, tibble, list with
x/yorlon/latcomponents, or a length-2 numeric vector for a single point- target
target CRS string (default
"EPSG:4326"). Must be geographic.- ...
ignored
- source
source CRS string (required). Must be a projected CRS.
Examples
## regular grid in UTM zone 55S, unprojected to lon/lat for tissot()
xy <- expand.grid(x = seq(4e5, 6e5, length.out = 5),
y = seq(5200000, 5400000, length.out = 4))
ll <- tissot_unproject(xy, source = "EPSG:32755")
tissot(ll, "+proj=utm +zone=55 +south")
#> Tissot indicatrix: 20 points, +proj=utm +zone=55 +south
#> # A tibble: 20 × 14
#> x y dx_dlam dy_dlam dx_dphi dy_dphi scale_h scale_k scale_omega
#> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl>
#> 1 146. -43.3 0.728 1.08e- 2 -0.0147 0.998 1.000 1.000 0
#> 2 146. -43.4 0.728 5.38e- 3 -0.00737 0.998 1.000 1.000 0
#> 3 147 -43.4 0.728 0 0 0.998 1.000 1.000 0
#> 4 148. -43.4 0.728 -5.38e- 3 0.00737 0.998 1.000 1.000 0
#> 5 148. -43.3 0.728 -1.08e- 2 0.0147 0.998 1.000 1.000 0
#> 6 146. -42.7 0.735 1.06e- 2 -0.0144 0.998 1.000 1.000 0
#> 7 146. -42.8 0.735 5.32e- 3 -0.00722 0.998 1.000 1.000 0.000000854
#> 8 147 -42.8 0.735 2.78e-12 0 0.998 1.000 1.000 0
#> 9 148. -42.8 0.735 -5.32e- 3 0.00722 0.998 1.000 1.000 0.00000148
#> 10 148. -42.7 0.735 -1.06e- 2 0.0144 0.998 1.000 1.000 0
#> 11 146. -42.1 0.742 1.05e- 2 -0.0141 0.997 1.000 1.000 0.000000854
#> 12 146. -42.2 0.742 5.26e- 3 -0.00707 0.997 1.000 1.000 0
#> 13 147 -42.2 0.742 0 0 0.997 1.000 1.000 0.00000121
#> 14 148. -42.2 0.742 -5.26e- 3 0.00707 0.997 1.000 1.000 0
#> 15 148. -42.1 0.742 -1.05e- 2 0.0141 0.997 1.000 1.000 0
#> 16 146. -41.5 0.749 1.04e- 2 -0.0138 0.997 1.000 1.000 0
#> 17 146. -41.6 0.749 5.20e- 3 -0.00692 0.997 1.000 1.000 0.00000121
#> 18 147 -41.6 0.749 2.78e-12 0 0.997 1.000 1.000 0
#> 19 148. -41.6 0.749 -5.20e- 3 0.00692 0.997 1.000 1.000 0.00000148
#> 20 148. -41.5 0.749 -1.04e- 2 0.0138 0.997 1.000 1.000 0.000000854
#> # ℹ 5 more variables: scale_a <dbl>, scale_b <dbl>, scale_area <dbl>,
#> # angle_deformation <dbl>, convergence <dbl>