Markers to print
Two pages. Print them and the tracer can pin your reference to the paper instead of to the screen — move the phone, tilt it, lean in on a detail, and the image stays on the sheet.
Free, like everything else here. One sheet of paper.
How to use them
- Print the sheet at 100% and check the ruler with a real one.
- Tape it down where you are going to draw.
- Open the tracer, load your reference and start the camera.
- Frame the whole sheet and press Anchor.
- Now move around. Keep at least one marker in view.
That last one is the whole trick
The camera has to see a marker to know where the paper is. That is why the sheet has eight of them around the edge: your hand covers one, leaning in cuts out three, and there is still one left. If they all leave the frame the image freezes where it was — it does not jump — and it picks back up the moment a marker returns.
Printing it right
- Print at 100%. If the dialog offers «fit to page» or «shrink to fit», turn it off — it shrinks by about 6% and every measurement stops being true.
- Measure the 100 mm ruler with a real ruler. If it does not read 100, print it again.
- Matte paper. Glossy and coated stock catch the lamp, and the glare eats the marker exactly where the light hits.
- Solid black. A cartridge running out leaves the border grey and broken.
The header strip
Two markers on one small piece of paper. Cut it out, tape it along the top edge of your paper, and the reference hangs below it — as wide as the strip, already in the paper’s perspective. If all you want is a picture on a page, start here: nothing to place, nothing to teach it.
Why two markers and not one
A single marker anchors perfectly right beside itself and comes apart as you move away from it. Measured: holding the phone flat, a 20 mm marker extrapolated 12 cm down is off by 91 px, and 18 cm down by 258. A small square seen straight-on barely foreshortens, so there is nothing to measure the perspective from and the fit invents it — flat is the worst case, not the best. Two markers give a base as wide as your reference, and the same 18 cm drops to 6.9 px. Thirty-seven times better for one more piece of tape.
The frame sheet
Eight markers around a clear area, and you draw on the sheet itself. This is the one to start with: the tracer knows where these eight sit on the page, down to the millimetre, so it can work out the paper from any one of them.
The cut-outs
The same markers in three sizes, to cut out and tape around a canvas, a wall, a mug — anything that is not this sheet. Cut on the dashed line; the white margin is part of the marker. The 15 mm ones hold until the camera spans about 22 cm, the 25 mm about 37, the 35 mm about 52.
Teaching it where they are
Nothing knows where a cut-out is — you put it there. So the printed sheet teaches it: tape the cut-outs where you want them, leave the sheet in the frame too, and move the camera slowly so it sees the sheet and the cut-outs together for a few seconds. It works out where each one sits — to under half a millimetre in testing — and from then on any single cut-out holds the anchor by itself. Then take the sheet away. The small number next to the anchor badge counts how many it has learned.
It remembers for as long as the camera stays on. Stop it or flip it and the sweep has to happen again — the markers might not even be the same ones by then.
What these actually are
ARUCO_MIP_36h12 markers — 36 bits with a minimum distance of 12, so a pencil line will not be mistaken for one. The twenty printed here sit at distance 15 from each other counting all four rotations. Four identified corners are enough to work out where the plane is, which is why one visible marker holds the anchor.