mapTissot: Add Tissot Indicatrices to a Map In oce: Analysis of Oceanographic Data

Description

Plot ellipses at grid intersection points, as a method for indicating the distortion inherent in the projection [1]. (Each ellipse is drawn with 64 segments.)

Usage

 `1` ```mapTissot(grid = rep(15, 2), scale = 0.2, crosshairs = FALSE, ...) ```

Arguments

 `grid` numeric vector of length 2, specifying the increment in longitude and latitude for the grid. Indicatrices are drawn at e.g. longitudes `seq(-180, 180, grid[1])`. `scale` numerical scale factor for ellipses. This is multiplied by `min(grid)` and the result is the radius of the circle on the earth, in latitude degrees. `crosshairs` logical value indicating whether to draw constant-latitude and constant-longitude crosshairs within the ellipses. (These are drawn with 10 line segments each.) This can be helpful in cases where it is not desired to use `mapGrid` to draw the longitude/latitude grid. `...` extra arguments passed to plotting functions, e.g. `col="red"` yields red indicatrices.

Details

The purpose and interpretation are outlined in [1], but should also be self-explanatory.

Dan Kelley

References

1. Snyder, John P., 1987. Map Projections: A Working Manual. USGS Professional Paper: 1395 (available at pubs.usgs.gov/pp/1395/report.pdf).

See Also

A map must first have been created with `mapPlot`.

Other functions related to maps: `lonlat2map`, `lonlat2utm`, `map2lonlat`, `mapArrows`, `mapAxis`, `mapContour`, `mapDirectionField`, `mapGrid`, `mapImage`, `mapLines`, `mapLocator`, `mapLongitudeLatitudeXY`, `mapPlot`, `mapPoints`, `mapPolygon`, `mapScalebar`, `mapText`, `oceCRS`, `shiftLongitude`, `utm2lonlat`

Examples

 ``` 1 2 3 4 5 6 7 8 9 10``` ```## Not run: library(oce) data(coastlineWorld) par(mfrow=c(1, 1), mar=c(2, 2, 1, 1)) p <- "+proj=aea +lat_1=10 +lat_2=60 +lon_0=-45" mapPlot(coastlineWorld, projection=p, col="gray", longitudelim=c(-90,0), latitudelim=c(0, 50)) mapTissot(c(15, 15), col='red') ## End(Not run) ```

Example output

```Loading required package: gsw
```

oce documentation built on Aug. 29, 2017, 1:05 a.m.