Stereoscopic depth perception plays a vital role in photogrammetry, as it enables the formation of a 3-D stereo model by viewing a pair of overlapping photographs. The stereo model can then be studied, measured and mapped. In this study, the stereoscopic measurements of images from Ultracam-D digital camera, acquired at 10cm GSD are investigated by carrying out repetitive measurements of various geometric features by an experienced photogrammetrist. The features selected for measurements are having different contrast like dark tonal variations in shadows and bright tonal variations with bright background. The measurements are validated with that of ground values to evaluate the achievable horizontal and vertical accuracy. Traditional standards for map accuracy give the horizontal accuracy as 0.25mm of map scale and vertical accuracy in terms of contour interval. The study shows the images acquired with high radiometry and color information helps to measure the features in low contrast conditions with reasonable good accuracy. In this study the root mean square error (RMSE) achieved in different contrast conditions and for different geometrical features are 7.7cm in horizontal and 12.5cm in vertical. The results shows, by using 10cm GSD color data, geospatial information at 1:500 scale can be prepared with 0.5 m contour interval.
Stereo measurement, Ultracam-D camera, accuracy
