The WARP_TRI function returns an image array with a specified geometric correction applied. Images are warped using control (tie) points such that locations ( Xi, Yi ) are shifted to ( Xo, Yo ).
The irregular grid defined by ( Xo, Yo ) is triangulated using TRIANGULATE. Then the surfaces defined by ( Xo, Yo, Xi ) and ( Xo, Yo, Yi ) are interpolated using TRIGRID to get the locations in the input image of each pixel in the output image. Finally, INTERPOLATE is called to obtain the result. Linear interpolation is used by default. Smooth quintic interpolation is used if the QUINTIC keyword is set.
This routine is written in the IDL language. Its source code can be found in the file
subdirectory of the IDL distribution.
Set this keyword to use smooth quintic interpolation. Quintic interpolation is slower but the derivatives are continuous across triangles, giving a more pleasing result than the default linear interpolation.