Terrasolid, Bentley and IGI Detail a City Scale Gaussian Splat Workflow Over Tallinn

Terrasolid, Bentley Systems and IGI Systems have published figures from a joint webinar on city scale gaussian splatting production over the historic center of Tallinn, Estonia. Bentley added splat output to iTwin Capture Modeler as a technical preview in April 2025, and 3D Tiles and SPZ export followed that June.

The Tallinn survey was flown with an IGI UrbanMapper 2 Evo, which combines ultra high resolution nadir imagery, four oblique camera views, integrated LiDAR and GNSS/INS positioning in a single modular payload. The Tallinn block was flown at roughly 500 meters above ground level, producing imagery at 2 cm ground sampling distance and LiDAR at roughly 45 points per square meter. The dataset runs to roughly 1,700 aerial images at roughly 300 MB each.

Bentley iTwin Capture Modeler Flex carries the reconstruction, supporting automatic aerial triangulation, RTK and GNSS positioning, ground control points, camera calibration and LiDAR integration, with reality meshes, photogrammetric point clouds, true orthophotos and 3D Gaussian Splats as outputs. The documented sequence imports the imagery and the camera positions, configures camera parameters, runs aerial triangulation, defines reconstruction boundaries, generates the splats and exports to open formats such as PLY or 3D Tiles.

Medium quality splats over the Tallinn dataset took roughly 18 hours on Bentley Cloud against roughly six days on a single high end GPU workstation. At the highest quality settings, Bentley Cloud finished in roughly 2 days and 11 hours while the local workstation needed close to 17 days. What the presenters do not state is the GPU model, the cloud node count, or the cost of either run.

TerraSplat and TerraScan then merge the splat and the LiDAR into one hybrid point cloud in which, in Terrasolid's wording, "LiDAR points inherit Gaussian Splat attributes while preserving accurate geometry". The merged cloud carries facade detail and object recognition from the splat and ground detection, vegetation penetration and existing classification logic from the LiDAR, so poles, trees, buildings and infrastructure can be classified and inspected in the same view. TerraScan 026.008 added Cut, Copy and Paste point tools for manual splat scene editing.

IGI also showed multi frequency GNSS analysis that continues processing on the frequencies left unaffected when satellite signals are jammed or spoofed, tested over both jammed and non jammed areas of Estonia, with degraded direct georeferencing still described as accurate enough for aerial triangulation and LiDAR strip adjustment. IGI Overlay Rotation Correction performs forward motion compensation by rotating the camera mount according to aircraft speed, altitude and direction, which IGI credits with sharper imagery and higher quality splats.

The recap gives no version number for TerraSplat, TerraScan or iTwin Capture Modeler Flex, and every timing in it is presenter supplied. The full write-up is available on Terrasolid's site.