AffineTransform

  • Affine transform uses a 2x3 matrix to define how pixel locations (u, v) correspond to locations in a Coordinate Reference System (CRS).

  • Pixel coordinates start at (0, 0) for the top-left corner of the image and (width, height) for the bottom-right corner, using the "PixelIsArea" raster space.

  • The translateX and translateY values represent the origin of the pixel grid within the CRS.

  • scaleX and scaleY represent pixel size when there's no rotation or shear, with scaleY often negative to position the (0, 0) pixel in the north-west.

  • This transformation is described by a JSON object containing six values: scaleX, shearX, translateX, shearY, scaleY, and translateY.

The affine transform. The six values form a 2x3 matrix:

( ( scaleX, shearX, translateX )
  ( shearY, scaleY, translateY ) )

specifying a transformation such that given a pixel location (u, v), the corresponding location in the CRS is this matrix times the column vector (u, v, 1). Pixel coordinates use the "PixelIsArea" raster space, i.e. (0, 0) is the top-left corner of the top-left pixel, and (width, height) is the bottom-right corner of the image. (translateX, translateY) is the origin (in the CRS) of the pixel grid. If there is no shear or rotation, then (scaleX, scaleY) is the pixel size. scaleY is often negative so that the (0, 0) pixel corner can represent the north-westernmost corner of the image.

JSON representation 
{
  "scaleX": number,
  "shearX": number,
  "translateX": number,
  "shearY": number,
  "scaleY": number,
  "translateY": number
}
Fields
scaleX

number

The horizontal scale factor.
shearX

number

The horizontal shear factor for some, though not all, transformations.
translateX

number

The horizontal offset.
shearY

number

The vertical shear factor for some, though not all, transformations.
scaleY

number

The vertical scale factor.
translateY

number

The vertical offset.