Structure from Motion A New Technology to Create 3D Models from 2D Photographs

Structure from Motion (SfM) is a photogrammetric technique used to create 3D models and ortho-imagery from a series of overlapping photographs. The photos can be collected by hand-held cameras or by increasingly popular and useful drones. The SfM products allow users to visualize conditions quickly and more inexpensively than previous means. Northwest Hydraulic Consultants (NHC) has used SfM products for a variety of applications including assisting with construction oversight and developing and validating hydraulic models.

NHC first used SfM technology on a large estuary restoration project in Tillamook, Oregon. The 700-acre project involved removing a levee, which breached earlier than expected. As a result, the construction management team needed access to inundated land to determine what tasks had been completed by the contractor. Nearly 1,000 images were taken with NHC's drone and the images were run through the SfM process. This allowed the construction management team to browse a high-resolution ortho-mosaic of the project on their computer and determine if a project channel had been dug, a levee section removed, and a log jam placed.

A second project on Sunset Falls in Index, Washington, employed SfM to compile detailed ortho-imagery to calibrate a 3D Computational Fluid Dynamics (CFD) model of the waterfall. Tight geo-referencing of the final image was needed, so ground control points were surveyed in advance of the 300 drone photos to provide exact scale, orientation, and position of the final product.

Finally, on the South Fork Clearwater River in Idaho, NHC used SfM to confirm a probable barrier to upstream fish migration. Combined with minimal traditional survey, more than 2,000 photographs taken from NHC's drone were processed to develop a terrain surface of the exposed riverbed. The terrain model was the basis for a 2D hydraulic model of the reach that provided context for fish migration models. A link to the hydraulic model results is found here.

Our experience shows that SfM has a wide range of applications in hydraulic analysis, modeling, and design. For further information, contact Chris Long or Erik Rowland at 206.241.6000.

    
SfM derived terrain and imagery allows NHC's client to visualize the modeled river conditions
that replicate those in a photograph they took.