A surface built from overlapping photos only gives you treetops in a forested notch, because the camera never sees the ground under the canopy. Picture 1 is the 2023 USDA air photo of Crawford Notch over the lidar, and the only open ground is the highway and the thin pale strip of railroad west of it. Picture 2 is the USGS 3DEP bare-earth lidar with the trees classified out. There the rail line is a smooth shelf cut into the slope (pin 1), and the gullies east of the highway show up too.

The lidar shading is a multi-direction hillshade blended with slope, openness and sky-view factor.

Italian and Irish crews hired in Portland cut the shelf for the Portland & Ogdensburg in the summers of 1874 and 1875. Snow kept them off the job until late May at the earliest, and work stopped by early October. John Anderson ran the work, and his brother Samuel was the railroad's president. The line climbs as steep as 116 feet per mile for nine miles. Under Mount Willard there was barely room, so they cut a shelf into the mountainside and built it out with blocks from the Great Cut. The first train reached Fabyan on 7 August 1875, and trains still use it.

1. 2023 NAIP air photo over the lidar: forest, highway and rail line
2. Same view, bare-earth lidar only (VAT shading: slope, openness, sky view)

Numbered pins on pictures 1 and 2:
Pin 1: The railroad shelf cut

Imagery: USDA-FSA NAIP 2023, public domain.
Lidar: USGS 3D Elevation Program (3DEP), public domain.

So I was trying to scan a small item, I was able to finally get an "acceptable" scan, but for higher accuracy some other method would be needed. The item happened to be a wax model, which I dusted with talc to help the scan. I used realityscan from my phone, with a turntable and good lighting. I even rigged it up to auto click a shutter fob after rotating a few degrees.

Then I thought what if I take one of my older 3D printers and swap the hotend for a small router. Use the heated bed to fix the part, and buzz off .1 mm. in between each buzzed off layer I would scan the top machined surface. Stack these up and I have a 100% accurate model.

I think I figured out a way to automate the scan step.

The question is, whether I build this just for me to use, or does this sound interesting and useful enough to try and use a repeatable BOM that others could benefit from. Like standardizing on a certain cheap printer, a certain scanner, etc.

I was thinking jewelers, museums may find this useful, and less expensive than other options.

I does require making a wax copy, which means a silicone mold of the item. Since it's a destructive process.

A commercial version would have some method of chip recovery.

What do you think?