Dealing With Large Images

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Many images that are useful in working with caves are extremely large. For example, the typical topographic map from the USGS is over 5,500 by 6,700 pixels in size. This is more than 36-million pixels in size or over 110-million bytes.


This can cause two problems. First, this is a significant portion of the typical computer’s memory. As a result, the computer may have to rearrange memory every time Compass manipulates the image. Second, just handling those 110-million bytes takes time. In order to lock the image to the cave plot, Compass has to scale, rotate and offset the image every time the view changes. As a result, it can take several seconds to display the image depending on the size of the image, the speed of the computer and the amount of memory available. Here are some strategies for dealing with the problem:


Resizing. In order for Compass to display images rapidly, you need to limit the image’s width and height to less than 3000 pixels. For this reason, every time you load an image in Compass gives you the option of clipping or resizing the image using the Image Editor.


Operating System. Windows 98 and ME have problems handling large bitmaps. For this reason, I would recommend using Windows 2000 or XP if you are working with large images.


Increasing Memory. Increasing the memory size can increase Compass’ speed displaying memory. I recommend 500-megabytes as the minimum for dealing with large images. One to two gigabytes is much better.