ISPRS-Annals ISPRS Annals of the Photogrammetry, Remote Sensing and Spatial Information Sciences ISPRS-Annals ISPRS Ann. Photogramm. Remote Sens. Spatial Inf. Sci. 2194-9050 Copernicus Publications Göttingen, Germany 10.5194/isprs-annals-XI-2-2026-29-2026 The Project evalAT for Investigating the Accuracy of Aerotriangulations in Map Projections Ressl Camillo https://orcid.org/0000-0002-3716-8961 1 Pfeifer Norbert 1 Ressl Christine 2 Bayr Andreas 2 TU Wien, Department of Geodesy and Geoinformation, Research Unit Photogrammetry, Wiedner Hauptstraße 8-10, 1040 Wien, Austria BEV – Federal Office of Metrology and Surveying, Department G2 – Remote Sensing, Schiffamtsgasse 1-3, 1020 Wien, Austria 03 07 2026 XI-2-2026 29 35 Copyright: © 2026 Camillo Ressl et al. 2026 This work is licensed under the Creative Commons Attribution 4.0 International License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/4.0/ This article is available from https://isprs-annals.copernicus.org/articles/XI-2-2026/29/2026/isprs-annals-XI-2-2026-29-2026.html The full text article is available as a PDF file from https://isprs-annals.copernicus.org/articles/XI-2-2026/29/2026/isprs-annals-XI-2-2026-29-2026.pdf

This paper investigates the accuracy of the aerial triangulation (AT) performed in a conformal map projection for a GNSS-INS-supported image block consisting of 4342 vertical images, GSD 20 cm, with 22 main strips and 5 cross strips. Using 169 check points the obtained results are compared with the accuracy achieved by running the AT in an undistorted tangential system. It turns out, that in both systems the same accuracies can be achieved, with RMSE in (X, Y, Z) of (7, 10, 11) cm, if Earth curvature and scale distortion are correctly modelled in the map projection. If the scale distortion is not considered, then the RMSE in Z increases by 100% to 300% (depending on the height distribution of the GCPs). In AT software packages that do not consider the scale distortion a partial compensation is possible by either adapting the height of the projection centres or the principal distance leading to RMSE of around (10, 11, 15) cm.