## Photogrammetric Survey

After a more or less schematic analysis, we now continue with precise measurements in the nadir image PSP_003234_2210 from Mars Reconnaissance Orbiter taken on April 5, 2007, with its HiRISE camera. The image has a resolution of 3 meters per pixel and is 2048 pixel wide and 1532 pixel high, which is the range for pixel coordinates from top left to right and from top to bottom (raw image 20.480 x 15320, 30cm per pixel). On the image southern outer arc, southern inner arc and northern outer arc can be clearly identified as landform marks.

The examination of the arc’s parameters can be done with usual photo editing software. After a download of the image from the internet image catalog page, single pixels are turned to white to indicate the positions of virtual survey stakes in the edges of the slopes. We take the coordinates of the virtual survey stakes and try to determine a circle of best fit to their positions with a Least Square Method. A suitable algorithm for circles of best fit is found in a javascript program of the University of Bayreuth, which uses a linear regression algorithm of Ian D. Coope, University of Canterbury in New Zealand, published in 1993 in Journal of Optimization Theory and Applications. This program needs a set of points and gives back center and radius for the circle of best fit.