What type of transformation is used when 10 control points are applied in georeferencing?

In georeferencing, when 10 control points are applied, a 3rd Order polynomial transformation is often used. This type of transformation allows for a more complex relationship between the source coordinate system and the target coordinate system. With a 3rd order polynomial, the transformation can account for curvature and non-linear distortions that may be present in the data.

Generally, the more control points you have, the higher the order of the polynomial that can be employed, which results in a more flexible transformation. A 3rd order polynomial involves terms that include squares and cubes, enabling the adjustment of the shape of features in the coordinate system to better match their real-world counterparts. This suitability for dealing with more complex spatial relationships is critical in obtaining accurate georeferencing results.

In contrast, a simple transformation or affine transformation would be more linear and typically requires fewer control points, making them less capable of addressing intricate spatial anomalies compared to a 3rd order polynomial. While a 2nd order transformation allows for some curvilinear adjustments, it is not as flexible as a 3rd order transformation, which is better for interpolating the complexities reflected in a larger number of control points. Hence, using 10 control points is well-suited for