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.
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 bysrs_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) orFALSE
to use authority compliant axis order (see Note).
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).
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)
.
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")
#> [1] -180.00000 -90.00000 180.00000 -48.65641
# authority compliant axis ordering
transform_bounds(bb, "EPSG:32761", "EPSG:4326",
traditional_gis_order = FALSE)
#> [1] -90.00000 -180.00000 -48.65641 180.00000