Abstract: Sparse distribution of image control points is critical for enhancing the economic efficiency of large-scale digital aerial photography.Based on the requirement for constructing a 1∶2000 high-precision real-scene 3D monitoring baseplate within the natural resources survey and monitoring system of the Inner Mongolia Autonomous Region,this paper designs 11 sets of comparative experiments with varying combinations of along-track baseline span and cross-track flight-line span to quantitatively verify the impact of spacing configurations on aerial triangulation accuracy.Results indicate that residual errors of orientation points remain minimally affected by span variations and checkpoint accuracy decreases with increasing spans,where plane accuracy shows higher sensitivity to along-track spans,while elevation accuracy responds more significantly to cross-track spans.Accordingly,span thresholds for image control point distribution balancing accuracy and efficiency in flat terrains are proposed,providing an engineering decision-making basis for precision-economy equilibrium in digital aerial photography.

Key words: image control points, aerial triangulation, along-track baseline span, cross-track flight-line span, normalized error increase rate, sparse distribution