Return MGRS grid reference precision (in meters)

Description

MGRS coordinates represent a "square" with a certain level of precision. See Details for more info.

Usage

mgrs_precision(x)

Arguments

Details

An MGRS grid reference is a point reference system. When the term 'grid square' is used, it can refer to a square with a side length of 10 km (6 mi), 1 km, 100 m (328 ft), 10 m or 1 m, depending on the precision of the coordinates provided. (In some cases, squares adjacent to a Grid Zone Junction (GZJ) are clipped, so polygon is a better descriptor of these areas.) The number of digits in the numerical location must be even: 0, 2, 4, 6, 8 or 10, depending on the desired precision. When changing precision levels, it is important to truncate rather than round the easting and northing values to ensure the more precise polygon will remain within the boundaries of the less precise polygon. Related to this is the primacy of the southwest corner of the polygon being the labeling point for an entire polygon. In instances where the polygon is not a square and has been clipped by a grid zone junction, the polygon keeps the label of the southwest corner as if it had not been clipped.

For example (spaces used for clarity):

4Q

precision level 6x8 degrees (in most cases) - function returns NA for this

4QFJ

precision level 100 km

4QFJ 1 6

precision level 10 km

4QFJ 12 67

precision level 1 km

4QFJ 123 678

precision level 100 m

4QFJ 1234 6789

precision level 10 m

4QFJ 12345 67890

precision level 1 m

Value

data frame with grid_ref and precision columns. precision is in meters.

References

https://en.wikipedia.org/wiki/Military_Grid_Reference_System#Grid_zone_designation

Examples

grefs <- c("4Q", "4QFJ", "4QFJ16", "4QFJ1267", "4QFJ123678",
           "4QFJ12346789", "4QFJ1234567890")
mgrs_precision(grefs)