Warp Options in MapInfo Pro Advanced
To warp a raster dataset, you can choose one of the following transform types.
- Conformal - Conformal transformations preserve shapes and angles and may include a rotation, a scaling and a translation. Straight lines and parallel lines remain straight and parallel in the output image. A minimum of 2 control points are required for Conformal transformation.
- Affine - The Affine transformation preserves collinearity and ratios of distances which means all points lying on a straight line remain on a straight line and the midpoint of a line segment remains at the midpoint and parallel lines remain parallel after transformation. However, it may not preserve angles between lines or distances between points. A minimum of 3 control points are required for Affine transformation.
- Projective - Projective transformation is a linear transform. Projective transformation maps lines to lines which means straight lines remain straight after transformation but parallelism may not be preserved. Projective transformation can be used for scanned maps and imagery files. Projective transformation requires exactly 4 control points at the four corners of the raster. These points ought to be rectilinear in either the raster (pixel) space or the world coordinate space. You can use Projective transformation if the world coordinates are rectilinear and the pixel coordinates are skew. (Add illustrations below)
- 2nd Order Polynomial - Polynomial transformations are higher-order, non-linear transformations which can handle more complex local distortions. Polynomial transformations are commonly used for image registration and correction of distortions in remote sensing applications. Polynomial transformations are smooth and are also known as ‘rubber-sheet’ transformations as they enable parts of an image to be stretched or warped to fit the control points. A minimum of 9 control points are required for a 2nd Order Polynomial transformation.
- 3rd Order Polynomial - A minimum of 16 control points are required for performing the 3rd Order Polynomial transformation.
By default, Automatic is selected which applies a linear transformation. A linear transformation is defined by a scaling factor and two pairs of common coordinates or one pair of coordinates and a bearing difference. This transformation provides only rotation and shift. In the Automatic mode, MapInfoPro Advanced will analyze the control points provided by you and choose the most suitable transformation for your data.