3D Laser Scanning
Monteath & Powys were approached to map the rock faces on either side of the cutting forming the southern on-ramp to the Sydney Harbour Bridge. Along with an accurate 3D model of the rock face itself, the client required high quality imagery which could be flattened and used as a background for the design of geotechnical rectification works.
Being a curved cliff face with limited access, this project provided many challenges which needed to be overcome in order to provide our client with an accurate and fit for purpose solution.
The designers were aware of our 3D & Spatial data capabilities and, for this reason, approached us to provide an innovative solution to this complex project. Several difficulties were encountered along the way, mostly due to site access restrictions, with no access to the road below, limited ability to place accurate survey control and the shadowing created by the cutting itself.
In previous projects, Monteath & Powys have utilised photography from a variety of angles to produce accurate complex meshes of similar structures. This project was slightly different, as we were limited to a single vantage point, on top of the opposing cliff face, to capture all photography. This meant instead of capturing imagery perpendicular to the surface, we were faced with an oblique angle as we looked down from the top of the cutting. In addition, the curved nature of the cutting prevented perpendicular photography at any point, further complicating the re-construction.
3D laser scanning was utilised in the first instance to capture the cliff face from within the Fort Street Public School on the inside of the loop and the footpath at the top outside of the cutting.
Now that we had a solid survey base to work from, we could address one of the primary objectives of the project and produce survey accurate, orthorectified imagery of the cliff faces in a format useable as a background map for design drawings and mark-up style geotechnical design in PDF drawings.
The most unusual component of this project was the straightening or flattening of a curved ortho-mosaic image. We believe the resulting flat image is suitable for designers to use as a direct design tool for completing red pen mark-ups and providing a raster behind design models. The ortho-mosaic provided the ability to take accurate and easily recognisable measurements directly on the image.
Monteath & Powys were now able to produce the final reports which consisted of high resolution orthorectified TIFF images, as well as a series of cross-sections produced on both the inside and outside cliff faces.