Stereo Photogrammetric Errors in Determining the Surface Area of a Small Pig Model with Non-Metric Cameras.

Abstract

A small pig model was made with plaster and plastic from the mold of a female pig of 27 days old. Surface area of the pig model was estimated with 2 non-metric cameras by stereo photogrammetry, and the error of surface area was analyzed. Error consists of optical error in determining the space coordinates of the pig model and shape error in tracing the complex shape of the object. Optical error was estimated with 28 control marks set around the pig model to calculate the space coordinates of about 300 object marks on it from stereo pairs of photographs. The objects marks were used for drawing cross sectional shape and contour lines of the pig model and estimating the surface area. Shape error was evaluated in comparison with the measured surface area by counting the numbers of a 1mm square section of the graph paper covering the pig model.The errors in the X- and Y-axes coordinates of the control marks were within 1mm. The errors in the Z-axis coordinates were in less than 3mm, distributing nearly equally in positive and negative. These errors were no more than theoretical limits. The error would give rise to about 5% of optical error, when estimating the surface area of a part in the body, formed with neighboring cross sections and assumed a truncated cone, 70mm and 66mm in radiuses and 27mm in slant length. Optical error could be neglected when the significant figures of surface area was limited to minimum.The difference between the measured and estimated total surface area of the pig model was 34cm2, which was only 1.2% on a relative basis. This means that the shape error was very small and the stereo photographs using the non-metric cameras was accurate enough.