5.2 Scrolling

Closely linked to the zooming feature is scrolling. Scrolling permits the user to view portions of the image that may have overflowed the image area. This operation is accomplished through the use of the two scrollbars bordering the right side and the bottom of the image area. The bottom scrollbar slides the image left and right, and the vertical scrollbar moves the image up and down. There are several ways to scroll the image with the mouse:

(1) Click or click and hold on the arrows of the scrollbar slider to smoothly scroll the image.

(2) Drag the scrollbar slider to a new location and release it.

(3) Click on the `anchor' boxes on either end of the scrollbar to move to one extreme or the other.

(4) To drag the image, hold down the Meta key (diamond key on Sun keyboards) and the left mouse button while moving the cursor in the image area.

Scrolling comes into play when you have zoomed in on an image. The zoom function uses a user-settable parameter called the retention factor to decide how much of the original image should be retained off-screen. For instance, if the retention factor is set to 2, when you zoom in, SatView will retain twice as much information in each direction as will fit in the image area. You may view this hidden portion of the picture by scrolling to it.

The performance of scrolling on a particular computer system depends on the resources of that system. Preserving data off-screen is very expensive memory-wise. If your system cannot provide the memory required to maintain information off-screen, performance will suffer. If you find that the scrolling is not smooth, you may just want to set the retention factor to 1, and not try to scroll the image. Be warned that the performance of the scrolling feature will vary widely depending on the system used.