In the section that follows the term ins is used to denote your insulin file. Change the commands given there to reflect the actual name of your insulin control file. ins is used throughout this section to refer to the name of this control file which is then used as the filename for all the other program operations in this series of tasks.

The Povscript program creates beautiful images. It does require some understanding of how it works however in order to get exactly the final image you want. The program uses the location of a camera to generate the image. The default lines relating to this in the pov file are given below.

   camera { location <0, 0, 20>
            look_at <0, 0, 0>
            up y
            right 3/2*x }   

The last number in the location line gives the position of the camera in the scene. This number is a good starting point. You will need to change this number to zoom in or back off from your molecule in order to get the entire structure on the shot.

The lines up y and right 3/2*x refer to coordinate system used in the program. If you use other height and width values than are given in the x-povray line in the manual, you will need to change the 3/2 value to reflect this change so that there is no distortion in the x and y directions of the picture. For example, creating an image with the values +W900 +H1200 in the x-povray line would require the 3/2 to be changed to 3/4 .

A series of images files have been included in this exericse to help explain the common problems encountered when using the program.

cram.ps-molscript - This is the reference molscript file on which the
		    comparisons are based. It is viewable with Ghostscript
		    (gs).

cram.tga-20 - 	    This file shows what happens to an image when the
		    camera is too close to the subject. View with xv.

cram.tga-30 -       This image is the result of backing the camera off a
		    little (from a value of 20 to 30) so that the entire
		    structure in now in the picture. View with xv.

Perspective is a problem with this software. Even when you have moved the camera position off so that the entire structure is in the shot, because of the depth of the molecule, distortions may still occur due to the unequal distance of the camera from all parts of the molecule. To counteract this an angle value is put into the camera control section. The smaller the angle the more the final image has the same orientation of the original Molscript image on which the process is based. However, the smaller the angle the more the camera has to be pulled back from the scene to get the desired result. In the case shown the value went from 30 to 3000.

   camera { location <0, 0, 3000>
            look_at <0, 0, 0>
            angle .5
	    up y
            right 3/2*x }   

cram.tga-3000 -     The image using the angle and large pull back to get
		    the desired final image. View with xv.