transform_bounds: Transform boundary

In gdalraster: Bindings to 'GDAL'

Transform boundary

Description

transform_bounds() transforms a bounding box, densifying the edges to account for nonlinear transformations along these edges and extracting the outermost bounds. Wrapper of OCTTransformBounds() in the GDAL Spatial Reference System API. Requires GDAL >= 3.4.

Usage

transform_bounds(
  bbox,
  srs_from,
  srs_to,
  densify_pts = 21L,
  traditional_gis_order = TRUE
)

Arguments

bbox	Numeric vector of length four containing the input bounding box (xmin, ymin, xmax, ymax).
srs_from	Character string specifying the spatial reference system for pts. May be in WKT format or any of the formats supported by srs_to_wkt().
srs_to	Character string specifying the output spatial reference system. May be in WKT format or any of the formats supported by srs_to_wkt().
densify_pts	Integer value giving the number of points to use to densify the bounding polygon in the transformation. Recommended to use 21 (the default).
traditional_gis_order	Logical value, TRUE to use traditional GIS order of axis mapping (the default) or FALSE to use authority compliant axis order (see Note).

Details

The following refer to the output values xmin, ymin, xmax, ymax:

If the destination CRS is geographic, the first axis is longitude, and xmax < xmin then the bounds crossed the antimeridian. In this scenario there are two polygons, one on each side of the antimeridian. The first polygon should be constructed with ⁠(xmin, ymin, 180, ymax)⁠ and the second with ⁠(-180, ymin, xmax, ymax)⁠.

If the destination CRS is geographic, the first axis is latitude, and ymax < ymin then the bounds crossed the antimeridian. In this scenario there are two polygons, one on each side of the antimeridian. The first polygon should be constructed with ⁠(ymin, xmin, ymax, 180)⁠ and the second with ⁠(ymin, -180, ymax, xmax)⁠.

Value

Numeric vector of length four containing the bounding box in the output spatial reference system (xmin, ymin, xmax, ymax).

Note

traditional_gis_order = TRUE (the default) means that for geographic CRS with lat/long order, the data will still be long/lat ordered. Similarly for a projected CRS with northing/easting order, the data will still be easting/northing ordered (GDAL's OAMS_TRADITIONAL_GIS_ORDER).

traditional_gis_order = FALSE means that the data axis will be identical to the CRS axis (GDAL's OAMS_AUTHORITY_COMPLIANT).

See https://gdal.org/en/stable/tutorials/osr_api_tut.html#crs-and-axis-order.

See Also

srs_to_wkt()

Examples

bb <- c(-1405880.71737, -1371213.76254, 5405880.71737, 5371213.76254)

# traditional GIS axis ordering by  default (lon, lat)
transform_bounds(bb, "EPSG:32761", "EPSG:4326")

# authority compliant axis ordering
transform_bounds(bb, "EPSG:32761", "EPSG:4326",
                 traditional_gis_order = FALSE)

gdalraster documentation built on June 8, 2025, 12:37 p.m.