Passive Ranging Devices and Related Systems, Methods, and Software

A range finding device, comprising:

• a range finding unit operable to determine an estimated range to a target object;
• an orientation sensor operable to determine an estimated bearing to a target object;
• and
• a target object location area calculation unit for determining a target location area, defined by near, far and side edges, from an estimated range and bearing to a target object, the target object location area calculation unit comprising:
• a far and near edge calculation module operable to calculate near and far offsets from the estimated range to thereby define near and far edges of the target object location area;
• and
• a side edge calculation module operable to calculate radii angularly offset from the estimated bearing and having a common origin with the estimated bearing to thereby define side edges of the target object location area;
• wherein the range finding device comprises:
• an imaging device operable to receive light incident on a primary aperture and generate a corresponding output image at a viewing aperture;
• a user actable scale input;
• and
• a range estimation module operable to:
• insert a scale marker into the output image;
• vary the size of the scale marker within the output image in response to user actuation of the scale input;
• and
• determine the size of the scale marker within the image and thereby determine an estimated range to the target object.