Charred Log

My photogrammetry skills are getting better thanks to some new equipment and a podcast that inspired me to invest in some new equipment. My first model armed with new knowledge and prototype equipment is a partially burned log from my fire pit.

For the last month, I have been working on a design for an automated photogrammetry turn table. The table is made from 3D printed components and uses an Arduino to rotate the table in small increments and then fire my Canon DSLR. The turn table is functional at this point, but I’m adding some additional features like a knob to control amount of rotation and a pause button.

In the middle of my build, I listened to Andrew Price discuss photogrammetry with Mason Menzies on the Andrew Price Podcast. The discussion is on YouTube and other podcast platforms. They discussed equipment, how to take good photogrammetry pictures and how to process the photos and models. To sum up the photography issues, you want your photos to have no shadow and no glare. You can achieve no shadows with a ring light and you can achieve no glare with cross-polarization.

Polarization limits light waves to a single plane. If you have a polarizer on you lens and another on your light, and the two polarizers are at 90 degrees from each other, then the glare is dramatically reduced.

After the discussion, I purchased a polarizing filter for my camera and a ring light. Mason actually suggests buying a 400w ring flash, but that sucker costs over $500, so I delayed this purchased. I wanted to make sure that cross-polarization made a significant difference.

I can definitely see the advantage to a 400w flash over a video lamp. First of all, the polarizing filter cuts down on a lot of light entering your camera. Plus, you need to overpower the room lights to remove the shadows and you can’t be too close to the subject. If your close to your subject, the front is much lighter than the back and this isn’t good for photogrammetry. The farther you move from you subject, the more consistent the light gets, but the less bright it is.

As a test of cross-polarization, I setup my camera with my new polarizing filter and a sheet spread across a flashlight. It works and I’m ready for the bigger investment.

Since I don’t have the flash yet, I was not able to reduce the glare I would like. To mitigate the glare problem, I purchased a can of vanishing scanning spray recommended by Mason. It made by AESUB and I purchased it on eBay. A single can cost me $50. Since this was a piece of junk wood and I didn’t need the spray to disappear, I probably should have just used Dr. Scholl’s foot spray.

I took 60 photos with the tripod set at one height. I then lowered the tripod and took another 60 photos. Then I lowered the tripod and took another 60 photos for a total of 180 photos.

The raw images were loaded into Adobe Lightroom, and as the Mason suggests, I cut down on the contrast by lowering the highlights and lifting the shadows.

The modified photos were loaded in Zephyr Lite for the photogrammetry calculation and then exported as an OBJ file. These files are being prepared to post on CGTrader.

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