I have to measure the distance between two cylinder legs. The platform sits on 4 legs and I need to measure a few feet underneath the bottom of the platform between the two north and south legs. What would be the best way to accomplish this with the most accuracy. I am looking to get as close to mm accuracy as possible.
Hi @CHUX! Welcome. I am guessing something like this?
I think some sort of orbital flight will be the way to go. This is an interesting case, but I would think two orbits at different elevations and camera gimbal pitches would be best. If you have the ability to create Ground Control Points on the four major corners that may be a big benefit to the accuracy. Without them and depending on how far apart the subjects are I wouldn’t be on much more than about 5-7cm of accuracy.
Are you looking for center-to-center or outside-to-outside?
It is more like this and they want to bring a specialized platform in between the legs within cm to minimize bumping due to sea conditions. The points would be closest inside points of the cylinders to each other.
I think that your beast measurement points are going to be towards the bottom of the piers where they hit the water. It would be tough to get much of anything underneath the platform. Also, because you will not be able to see the piers from a horizontal perspective you would need to analyze the point cloud in 3D as a section.
Honestly, to me it sounds like you need to just get a laser disto and actually shoot them. There are higher end ones that shoot further in case this one doesn’t shoot far enough.
We did think of that, however we would need rope access technicians or crazy scaffolding to access. I was told that I could take a series of photos, stitch them and then take a point to point measurement using this software. Is that information accurate?
Ok, gotcha. I was thinking of just trolling a boat over there, but I am not a regulations guy.
You can do as you were told, but mm accuracy is not very obtainable with photogrammetry unless it is a smaller subject and you can get very close to it.
agreed, Photogrammetry is not the solution here. If you cannot use a disto to measure between i would recommend doing a full 3d scan of the underside. it looks like there is access to below the main deck and you could mount a laser scanner somewhere there. Or use a total station and take a series of reflector less shots from that lower scaffold.
Yeah, after much research using a disto in some fashion will be our solution. Thank you all for your input.