APPENDIX C

Subpixel Accuracy

In the LAS 7.0, the location of a projection or other (X,Y) coordinate is defined to be located at the center of a pixel. The diagram that follows describes coordinate locations when dividing a pixel into subpixel increments.

To calculate subpixel values from an enlarged (interpolated) image window (as in tiepts), the following equation is applied:

               1        (x-1)  
   x' = .05 + ----   +  ----
              2*zoom    zoom


               1        (y-1)  
   y' = .05 + ----   +  ----
              2*zoom    zoom

where:

x and y          are integer image coordinates in the enlarged image

x' and y'        are noninteger image coordinates in the original image

zoom             is the enlargement factor