This icon or the Alternate Points File item in the Tools menu brings up the Alternate Point File dialogue box.
The upper portion of this box is for reference only and tells you the names of the current files (.BMP .PTS .ASR) and the number of points already mapped.
The middle section is also read-only indicating the Camera Definition and Database that are being used.
The lower portion allows you to select a point file and specify whether you want to Replace any points currently defined with those from the selected file or to Merge them together.
Occasionally, when you select a point file you will get a warning that the points are out of the range of the image. The reason for this is that the current image is smaller, in at least one dimension, that the image wherein the points were originally mapped. This is not necessarily an error.
See the section on using alternate point files for the possible uses of this feature.