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. Multiple bounding boxes may be given as rows of a numeric matrix or data frame. 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	Either a numeric vector of length four containing the input bounding box (xmin, ymin, xmax, ymax), or a four-column numeric matrix of bounding boxes (or data frame that can be coerced to a four-column numeric matrix).
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

For a single input bounding box, a numeric vector of length four containing the transformed bounding box in the output spatial reference system (xmin, ymin, xmax, ymax). For input of multiple bounding boxes, a four-column numeric matrix with each row containing the corresponding transformed bounding box (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.

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 Aug. 29, 2025, 5:15 p.m.