Whether you need scale for the measurement depends on the application, but most applications do need to scale the measurement. To get scale, you must provide V-STARS with at least one known distance between two measured points. You can specify a virtually unlimited number of scale distances, and we recommend you use at least two scale distances, whenever possible, to provide redundancy. Of course, the scale points are like any other points; they must be measured and triangulated. They do not have to be measured in all the photographs to be triangulated, and they do not have to be seen in the same photographs. They simply must be seen in at least two of the entire set of photographs so they can be triangulated. Of course, for best results, you should try to see them in at least three or more photographs with good geometry.
Often, to get scale for the measurement, bars with targets located on them at precisely known distances are placed on or around the object. This is often not a trivial matter. Placing the Scale Bars on or near the object without obscuring other targets or being itself obscured can sometimes be difficult. One must also be careful to ensure the scale targets fit onto the photographs since they often are placed around the periphery of the object, or extend outside the boundaries of the object being measured. For the best results, the Scale Bar(s) should be comparable to the size of the object being measured.
Finally, it is very important to realize the Scale Bar(s) must be rigidly attached to the object being measured. That is, a Scale Bar CANNOT move relative to the object being measured while the object is being measured. If it does move during this time, the scale measurements will be corrupted, and can’t be used. (If the Scale Bar has moved during the measurement, the operator will be able to detect the movement when looking at the measurement results).