Gradus Adeptus

Photograph something next to a coin or a credit card, measure the coin, mark the thing you are printing, pick the same two points on the model, and export a true-scale STL or GLB. The model on screen is never resized. Sizing a 3D print from a coin in a photograph could be a first for the whole industry. Of course, that only matters if it gets your print out of the slicer at the right size, and it does.

The workflow

• Select the tool. The measuring window opens by itself.
• Choose an image from disk, or pick one already loaded.
• Pick the known object from the list, or type a custom length in millimeters.
• Press Mark Known Object, then click the two ends of it in the photo: straight across a coin, along a card's long edge.
• Press Mark Target Object, then click the two ends of the thing you are printing.
• Press Pick Model Points on the option bar and click those same two spots on the 3D model. The tool disarms itself after the second click.
• The readout switches to the exported size, and the two export buttons come alive.

Option bar

• Setting - Which Gradus procedure to run: Resize From Image.
• Measure Photo - Opens the measuring window.
• Pick Model Points - Arms two clicks on the model. Clicking empty space disarms without recording. When the loaded model is a PhotoMesh built from this same photo, the two picks in the photo have already placed the model points, so this step is done for you and the button says so.
• Readout - Names the next step in words until the measurement is complete, then reads as the exported size, for example "Exports at 84.3 x 51.2 x 12.0 mm".
• Export STL - Writes the model at real size as a binary STL in millimeters, the unit every slicer assumes. Geometry only.
• Export GLB - Writes the model at real size as a GLB in meters, the glTF spec unit, with painted color included.

The measuring window

• Choose Image - Loads a photo from disk. A dropdown beside it picks from images already loaded.
• Known object - US Dime at 17.91 mm, US Nickel at 21.21 mm, US Quarter at 24.26 mm, a credit card's long edge at 85.60 mm, an AA battery at 50.5 mm, and US Letter paper's long edge at 279.4 mm. These are published specification sizes, not measurements of a sample.
• mm field - The known object's real length. Picking from the list fills it. Typing your own makes it a custom length.
• Mark Known Object - Then click the two ends of the known object in the photo. Click one end and drag to the other, or click each end.
• Mark Target Object - Then click the two ends of the object you are printing.
• Zoom - Magnification, from fit-to-frame upward.
• Resize grip - Drag to resize the window.

Notes

• Both picked points stay drawn over the viewport, joined by a line, the whole time the tool is selected.
• The picks are converted into export space at the moment you make them, so the scale factor describes the shape that actually goes into the file.
• Exporting needs a model loaded and a valid scale factor. Neither export ever resizes the model on screen.