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Create a square polygon (block) based on input coordinates and size

MakeBlockPolygon.Rd

This function creates a square polygon (block) that contains the input coordinates. The block is aligned to a grid defined by the size parameter, with the coordinates rounded to the nearest multiple of size. The resulting polygon is returned as an sf object.

Usage

MakeBlockPolygon(x, y, size)

Arguments

x

Numeric. The x-coordinate (e.g., longitude) of a point within the desired block.

y

Numeric. The y-coordinate (e.g., latitude) of a point within the desired block.

size

Numeric. The size (side length) of the square block in the same units as the input coordinates (e.g., degrees).

Value

An sf object representing the square polygon. The polygon is created in the WGS 84 coordinate reference system (EPSG:4326).

Details

The function calculates the lower-left corner of the block by aligning the input coordinates to a grid defined by the size parameter. For example:

  • If x = 5.2, y = 10.7, and size = 1, the lower-left corner will be at (5, 10).

  • The block will extend from (5, 10) to (6, 11).

  • If x = 5.2, y = 10.7, and size = 0.1, the lower-left corner will be at (5.1, 10.6).

  • The block will extend from (5.1, 10.6) to (5.2, 10.7).

The polygon is created with vertices in the following order:

  1. Lower-left corner (xll, yll)

  2. Lower-right corner (xll + size, yll)

  3. Upper-right corner (xll + size, yll + size)

  4. Upper-left corner (xll, yll + size)

  5. Lower-left corner (xll, yll) (to close the polygon)

The resulting polygon is returned as an sf object with a WGS 84 (EPSG:4326) coordinate reference system.

Examples

# Create a 1x1 degree block including the point (5.2, 10.7) aligned to a 1x1 degree grid:
block <- MakeBlockPolygon(5.2, 10.7, 1)
print(block)
#> Simple feature collection with 1 feature and 0 fields
#> Geometry type: POLYGON
#> Dimension:     XY
#> Bounding box:  xmin: 5 ymin: 10 xmax: 6 ymax: 11
#> Geodetic CRS:  WGS 84
#>                         geometry
#> 1 POLYGON ((5 10, 6 10, 6 11,...
plot(block)

# Create a 0.25x0.25 degree block including the point (5.2, 10.7) aligned to a 0.25x0.25 degree grid:
block2 <- MakeBlockPolygon(5.2, 10.7, 0.25)
print(block2)
#> Simple feature collection with 1 feature and 0 fields
#> Geometry type: POLYGON
#> Dimension:     XY
#> Bounding box:  xmin: 5 ymin: 10.5 xmax: 5.25 ymax: 10.75
#> Geodetic CRS:  WGS 84
#>                         geometry
#> 1 POLYGON ((5 10.5, 5.25 10.5...
sf::st_centroid(block2)
#> Simple feature collection with 1 feature and 0 fields
#> Geometry type: POINT
#> Dimension:     XY
#> Bounding box:  xmin: 5.125 ymin: 10.62501 xmax: 5.125 ymax: 10.62501
#> Geodetic CRS:  WGS 84
#>                 geometry
#> 1 POINT (5.125 10.62501)