No really, I mean literally, in the alley behind our building. The Washington State Department of Transportation (WSDOT) was scanning buildings in Post Alley between Madison and Spring this morning, creating LiDAR point clouds.

I ran into these guys a few months ago on my way to work, where the alley between First and Second meets University Street. As the technical writer here at LizardTech I’ve seen plenty of LiDAR data, but I’d never seen a LiDAR scanner before. I had once worked on a survey crew and used a theodolite, and thinking this was just a topographic setup I almost walked by these brightly vested crewmen and their tripod without a second thought. But then I noticed that the machine atop the legs was bigger than a theodolite and it was moving, very slowly, by itself. On the wall of the alley opposite the machine, a small green light pattern was flickering.

Since we make products for losslessly compressing and viewing LiDAR files, I was fascinated and engaged the men in conversation. On a laptop lying there on the cobbles and plugged into the scanner, they showed me how they programmed the machine using Leica software to scan from here to there, and at a desired density. A viewer enabled them to see the LiDAR data that was being captured right then, or an image of the alley from the perspective of the scanner, or both together.

They said they were scanning all the buildings within a certain radius of the Alaskan Way Viaduct, which, if you’re from around here, you know is due to come down soon and be replaced with something better, or at least something newer, safer and more expensive. WSDOT doesn’t want anyone coming back after the viaduct project saying that their activity caused their building’s walls to shift or its foundation to sink.

WSDOT has to take all these measurements in the warm weather of summer, then repeat them in winter, because buildings heat up and expand enough that their outer walls actually move. Also, down by the bay, the earth expands and contracts with the ebb and flow of the tides, so they’ll have to take measurements at high and low tides. It had not occurred to me that our buildings and even the ground they sit on were breathing in and out, as it were, with tide and temperature.

You could have knocked me over with a LiDAR point. 

Tags: Leica, LiDAR, Post Alley, Viaduct Replacement Project, WSDOT