Georeferencing GenAnywhere Scenes for OpenRoads: A Practical Pipeline

A developer documented a manual pipeline for georeferencing GenAnywhere's AI-generated textured meshes into Bentley's OpenRoads, treating the output as a visual reference rather than design geometry. The workflow sets and records the project CRS, converts the scene into that frame, anchors it with at least four spread control points, and requires plan residuals under five centimeters before use. On one corridor, a difference surface against surveyed terrain showed a mean deviation of 0.2 meters and a maximum of 1.8 meters at a tree line — usable as context, the developer noted, but "useless for a vertical curve.

The scene arrived in the right town, on the right block, and about four feet below the road. It also looked rotated by a degree or two. Nothing in the file said so. The mesh was beautiful, the textures were sharp, and every check I ran in the viewer came back green because the viewer had no idea what a datum was. GenAnywhere takes a map selection and returns a textured mesh of buildings, ground and vegetation fused together. It is produced from imagery and inference, not from control points. The export is a scene, not a geospatial dataset. There is no CRS field, no unit field, no list of objects. Treat it like a photograph that happens to have depth. Horizontal placement and vertical placement fail separately. Horizontally, the scene is usually close but not exact; it may use a local tangent plane, or a web projection that is not your project's state plane. Vertically, the difference is bigger. Imagery-derived ground is not a survey, and ellipsoid heights are not orthometric heights. A scene can be a meter low and still look perfectly flat. Units are the quiet third problem. I have seen a scene come in scaled by 3.28 because someone assumed meters, and the only symptom was a road that looked slightly wide. Fix the unit before the control points; otherwise the residuals will look terrible for a reason that has nothing to do with placement. Pick the project CRS before importing anything, and write it down. Convert the scene into that frame, then anchor it with at least four control points spread across the site, not clustered in one corner. I use monuments, bridge corners, or building corners that appear in both the survey and the imagery. Compute residuals. If they disagree by more than a few centimeters in plan, the fit is wrong, and no amount of visual tweaking will fix it. The mesh fuses roofs, walls, trees and terrain. For comparison, I extract a ground-only surface and leave the buildings as context. This is manual work, and it is the step people skip. A merged mesh will happily answer a ground query with a roof elevation, and your difference surface will look like a landslide. Once the scene is placed, I build a difference surface against the surveyed terrain. Mean and maximum deviation tell me whether the scene is usable as context. On this corridor, the mean was 0.2 meters and the maximum was 1.8 at a tree line. That is fine for a visual and useless for a vertical curve. In OpenRoads, the scene comes in as a reference, never as design geometry. I attach it to a layer named for the source and date, scale it correctly, and freeze it. The terrain surface, the alignment, the corridor and the drainage stay native. iTwin handles review; ProjectWise handles revisions. The reference is replaced when a newer scene is generated, and the design does not move. A corridor is not a mesh. OpenRoads carries templates, superelevation, stationing, utility crossings and rules. The scene carries pixels and triangles. There is no automatic conversion in either direction, and the attempts I have seen produce a model that looks right and cannot answer a single design question. The import is manual for a reason: it forces you to decide what the scene is allowed to influence. Decimation helps here. I cap the reference at a few hundred thousand triangles so the design file stays usable on a normal machine. Project CRS set and recorded. Scene converted and anchored to four or more control points. Residuals under five centimeters. Ground extracted. Difference surface checked. Scene attached as a frozen reference. Source date and imagery date written into the layer name. Every one of these takes minutes and saves days. A generated scene is excellent at answering what a place looks like. OpenRoads is the tool that answers where the road goes, how it drains, and what it costs. The seam between them is a coordinate system and a layer name. Get those two right, and the rest of the pipeline behaves.