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geo.regionAffineTransform

geo.regionAffineTransform(
   $region as cts.region,
   $transform as Object[],
   [$options as String[]]
) as cts.region

Summary

Perform an affine transformation on a geospatial region. The transformation is always applied in the raw coordinate system (Cartesian).

Parameters
$region
$transform A sequence of maps that specify the transformation to apply. Each map should contain at least one of the following transform specifications:
translation
Translate the points of the region by the given amount in the x and y coordinates. The value is a map with the following keys:
tx
Amount to shift the points in the x direction. (Required.)
ty
Amount to shift the points in the y direction. (Required.)
scaling
Scale the points of the region by the given amount of the x and y coordinates. The value is a map with the following keys:
sx
Amount to scale the points in the x direction. (Required.)
sy
Amount to scale the points in the y direction. (Required.)
psc
Point to scale relative to. (Optional. Default is the origin.)
rotation
Rotate the points of the region by the given angle. The value is a map with the following keys:
angle
Amount to rotate the points (radians). (Required.)
prot
Point to rotate relative to. (Optional. Default is the origin.)
shearing
Shear the points of the region by the given amounts. The value is a map with the following keys:
shxy
Amount of shearing due to x in y direction. (Required.)
shyx
Amount of shearing due to y in x direction. (Required.)
reflection
Reflect the points of the region around a line or a point. The value is a map with the following keys:
lineR
Line of reflection.
pref
Point to reflect points around. The value is a map with the following keys:
start
The starting point of the line.
end
The ending point of the line.
Exactly of lineR or pref must be specified.
If no transform specifications are provided, the points are transformed by the identity transform. That is, they remain unchanged.
$options Geospatial options that affect the transformation. Currently there are no relevant options.

Usage Notes

The ordering of transformations applied makes a difference. For example, scaling the point (1,1) by x=2 and y=3 and then translating it by x=1 and y=1 gives us the point (4,4). But translating it by x=1 and y=1 and then scaling it by x=2 and y=3 gives us (4,5). When multiple transformation are mentioned in a single map, the ordering is: translation, scaling, rotation, shearing, and then reflection. In general it is better to put separate transformations in separate maps in the sequence so there is no confusion. Transforms in the sequence are applied in order.

See Also

Example

// Reflection about the line from point (2.5,0) to point (2.5,2.0)
geo.regionAffineTransform(
  cts.polygon([
    cts.point(1.5,0),cts.point(2.5,1),cts.point(1.5,2),
    cts.point(0.5,2),cts.point(0.5,0),cts.point(1.5,0)]),
  {reflection: { lineR: {start: [2.5,0], end:[2.5,2.0]} }}
)

// => 3.5,0 2.5,1 3.5,2 4.5,2 4.5,0 3.5,0

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