On Earth, photogrammetrists can normally use manmade objects in their frame\u2014such as a road of known width or a curb of known height\u2014as scales. When none are present, they can insert such \u201cground truth\u201d as needed\u2014for example, by placing onto surveyed locations targets that will be visible in their images. On other planets in our solar system, however, such human artifacts are not (yet) available to photogrammetrists\u2014nor can they easily move cameras around to generate many images of the same spot from different angles.<\/p>\n
When NASA\u2019s Marshall Space Flight Center wanted to measure the depth of the craters created by the Curiosity Rover\u2019s landing in Mars\u2019 Gale crater from photographs taken by the rover\u2019s two navigation cameras (navcams), the only high precision scale information that photogrammetrists had was the distance between those cameras. The only other control data they had was the width of the rover tracks, which were visible in some of the imagery. To solve this puzzle, Cardinal Systems, a mapping software developer, created sophisticated new algorithms; these can now also be used to extract accurate measurements from photos taken with inexpensive consumer cameras and\/or from unstable platforms, such as small unmanned aerial systems (UAS) in strong winds.<\/p>\n