Photoclinometry
Encyclopedia
Photoclinometry is the process by which a 2-dimensional image of a surface is transformed into a surface map that represents different levels of elevation. It uses the shadows and light direction as reference points. It is used mostly to depict the surface of sculptures, to give an idea of how it would look in 3-dimension. The techniques depend on very specific conditions, especially light direction.
levels to depict the height of a point on a surface. Knowing the direction and angle of the light source, one can calculate the approximate height that a point has. However the light direction and angle is usually unknown, which leads to poor quality images, or having to create multiple bump maps, each time trying different settings.
In order to solve these problems, new missions to other planets plan to use a process similar to stereoscopy
in order to get a more accurate depiction of the surface on another planet. The Mars Reconnaissance Orbiter
is one of the mission that attempts to do this. This process uses two images of one location taken from two separate lens on a camera, much in the same way humans do with their eyes. By using two images, they can get a 3-dimensional perspective of objects on the surface like we do.
The Process
When light reflects off an object it creates shadows. These shadows can be used to create a bump map of a surface, which uses grayscaleGrayscale
In photography and computing, a grayscale or greyscale digital image is an image in which the value of each pixel is a single sample, that is, it carries only intensity information...
levels to depict the height of a point on a surface. Knowing the direction and angle of the light source, one can calculate the approximate height that a point has. However the light direction and angle is usually unknown, which leads to poor quality images, or having to create multiple bump maps, each time trying different settings.
Usage
- Some artists use photoclinometry to digitize a 3-dimensional representation of a sculpture.
- GeologistGeologistA geologist is a scientist who studies the solid and liquid matter that constitutes the Earth as well as the processes and history that has shaped it. Geologists usually engage in studying geology. Geologists, studying more of an applied science than a theoretical one, must approach Geology using...
s and those that study planetary sciencePlanetary sciencePlanetary science is the scientific study of planets , moons, and planetary systems, in particular those of the Solar System and the processes that form them. It studies objects ranging in size from micrometeoroids to gas giants, aiming to determine their composition, dynamics, formation,...
use it to get an idea of how the surface of a planet looks like, and generate topographic maps and digital elevation modelDigital elevation modelA digital elevation model is a digital model or 3-D representation of a terrain's surface — commonly for a planet , moon, or asteroid — created from terrain elevation data....
s.
Problems
Light direction is very important to the quality of a photoclinometric image. Light that comes from directly over the surface (behind the camera) makes it hard to distinguish the shadows. Multiple light sources are also a problem, since they destroy important shadows required for the algorithms to work properly.In order to solve these problems, new missions to other planets plan to use a process similar to stereoscopy
Stereoscopy
Stereoscopy refers to a technique for creating or enhancing the illusion of depth in an image by presenting two offset images separately to the left and right eye of the viewer. Both of these 2-D offset images are then combined in the brain to give the perception of 3-D depth...
in order to get a more accurate depiction of the surface on another planet. The Mars Reconnaissance Orbiter
Mars Reconnaissance Orbiter
Mars Reconnaissance Orbiter is a NASA multipurpose spacecraft designed to conduct reconnaissance and Exploration of Mars from orbit...
is one of the mission that attempts to do this. This process uses two images of one location taken from two separate lens on a camera, much in the same way humans do with their eyes. By using two images, they can get a 3-dimensional perspective of objects on the surface like we do.
Further reading
- Kirk, Randolph L., Barrett, Janet M., Soderblom, Laurence A. (2003) Photoclinometry Made Simple...? Advances in Planetary Mapping. http://astrogeology.usgs.gov/Projects/ISPRS/MEETINGS/Houston2003/abstracts/Kirk_isprs_mar03.pdf
- McEwen, Alfred S. (1991) Photometric functions for photoclinometry and other applications. Icarus, 92, 298-311. ISSN 0019-1035.
- Wilson, L., Hampton, J. S., Balen, H. C. (1985) Photoclinometry of Terrestrial and Planetary Surfaces. Lunar and Plantary Science, XVI, 912-913. http://adsabs.harvard.edu/abs/1985LPI....16..912W