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> The city used LIDAR technology, in which a drone or airplane shoots a light at the ground and the length of light is measured to determine elevation. The “pha
by sushisource 7y ago
> The city used LIDAR technology, in which a drone or airplane shoots a light at the ground and the length of light is measured to determine elevation. The “phantom hills” are recorded when the drone or airplane mistakes, say, a building’s shadow as a hill.
Uhhh... No? Lidar definitely wouldn't have that problem.
- farisjarrah 7y agoWould you mind educating us why? I cant seem to find info online immediately about shadows affects on lidar?
- saltcured 7y agoLIDAR doesn't really depend on any other illumination, so there are no shadows as such. If there is too much other illumination in the same wavelengths (or too little returned reflection) it might not register a return at all and this would appear as a hole in the data. If not shining straight down, it might have an error for the horizontal positioning of a building's roof, but it will still measure a discontinuity like a cliff edge where one measurement hits the roof elevation and the next hits the ground adjacent to the building. If measuring through a tree canopy, there will be multiple levels of returns as beams penetrate to different elevations before reflecting. These levels may include some measurement of the true ground level, unless the canopy is so dense that all beams hit a tree. So, a dense mass of trees or brush might obscure the true ground level beneath them. Perhaps the original article author conflated this with the idea of shadows.
- xgulfie 7y agoLidar captures a depth map and as such does have "shadowing" if you transpose an image taken from an angle to a vertical elevation map. Maybe that's what they meant, or that meaning got lost somewhere.