Autotek autocad raster design 2010 用户手册
There are two transformation methods you can use to correct your image:
■
The Triangular method draws a series of triangles between the control
points, then applies the transformation to those areas. This process uses
the Delaunay triangulation method in which no point lies inside the circle
that includes the vertices of any triangle. Each triangular area is transformed
separately, so this method is much more accurate than the polynomial
method, but can result in the loss of some image data. The area to be
transformed, called the convex hull, is defined by the outermost destination
points. Image data outside the convex hull is discarded. You can see which
portion of the image will be transformed using the Preview. If you want
to preserve more of the image data, place control points near the extents
of the image.
points, then applies the transformation to those areas. This process uses
the Delaunay triangulation method in which no point lies inside the circle
that includes the vertices of any triangle. Each triangular area is transformed
separately, so this method is much more accurate than the polynomial
method, but can result in the loss of some image data. The area to be
transformed, called the convex hull, is defined by the outermost destination
points. Image data outside the convex hull is discarded. You can see which
portion of the image will be transformed using the Preview. If you want
to preserve more of the image data, place control points near the extents
of the image.
■
The Polynomial method transforms the entire image to match, as nearly
as possible, the control points you specify. Unlike the triangular method,
however, the actual destination points are not always located at the
destination points you specified. The resulting positional error is expressed
as a numerical value in the Rubbersheet dialog box, and is displayed
graphically on the image after the control points have been entered. As
shown in the following figure, the error for each point is measured as a
distance from the intended destination point to the actual destination
point.
as possible, the control points you specify. Unlike the triangular method,
however, the actual destination points are not always located at the
destination points you specified. The resulting positional error is expressed
as a numerical value in the Rubbersheet dialog box, and is displayed
graphically on the image after the control points have been entered. As
shown in the following figure, the error for each point is measured as a
distance from the intended destination point to the actual destination
point.
The error is calculated using the following distance formula:
The total RMS (Root Mean Square) error of the image is calculated using the
following formula:
following formula:
32 | Chapter 2 Inserting and Correlating Images