Editing Tools

How to Automatically Scale Photogrammetry Captures with AprilTags

Polycam can automatically scale your photogrammetry captures to real-world dimensions using a printed AprilTag. Place a single tag in your scene as you capture, and Polycam uses it as a known reference measurement to size your entire model, with accuracy typically greater than 99%. In this article you will learn how to choose the right tag size, print it at the correct scale, and capture it for accurate results.

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Automatic rescaling is available for photogrammetry captures only.

Important: The printable tags are available to download by anyone, but automatic scaling only runs on Business and Enterprise accounts. On any other plan, a tag included in your capture will be photographed like any other object in the scene and your capture will not be scaled.

How Automatic Scaling Works

An AprilTag is a high-contrast square marker, similar in appearance to a QR code, that software can detect and measure precisely. Because Polycam knows the exact printed size of each tag, it can compare that known measurement against the tag as it appears in your photos and calculate the true scale of the entire capture.

Place one printed tag in your scene, capture it in at least eight photos, and your finished model is scaled to real-world dimensions automatically. There's nothing to enable or toggle, and no manual measurement or rescaling is required.

A printable Polycam AprilTag with a six-inch measurement scale printed beneath it — Each printable tag includes a measurement scale beneath it, used to confirm the tag printed at its correct size.

Important: Use only one tag per scene. Automatic scaling will not work if more than one tag appears in your capture.

Download the Printable Tags

Choose the tag size that fits the scale of your scene, then download and print it. Tags are available in both imperial and metric sizes.

Imperial Sizes

Tag Size	Printed Scale	Copies per Sheet	Paper Required	Download
2 × 3 in	1.5 inches	9	US Letter	PDF
4 × 6 in	3 inches	2	US Letter	PDF
8.5 × 11 in	6 inches	1	US Letter	PDF
11 × 14 in	8 inches	1	11 × 14 in	PDF
12 × 18 in	9 inches	1	12 × 18 in	PDF
18 × 24 in	12.5 inches	1	18 × 24 in	PDF

Metric Sizes

Tag Size	Printed Scale	Copies per Sheet	Paper Required	Download
A8	1.5 inches	9	A4	PDF
A6	3 inches	2	A4	PDF
A4	6 inches	1	A4	PDF
A3	8 inches	1	A3	PDF
A2	12.5 inches	1	A2	PDF

Choosing the Right Size

Scaling accuracy depends on Polycam being able to resolve the tag's corners clearly in your photos, so the larger your scene, the larger your tag needs to be.

Small objects and close-range captures: The smaller sizes work well, such as 4 × 6 in or A6
Window-scale scenes and larger: Use a tag with a printed scale of 6 inches or more, meaning 8.5 × 11 in or A4 and up

Tip: If you're unsure, size up. A tag that's larger than necessary still scales accurately, while a tag that's too small for the scene won't resolve well enough to produce a reliable measurement.

How to Scale a Capture with an AprilTag

1Print Your Tag

Once you've chosen a size, print it using the settings below. Each tag has a measurement scale printed alongside it that you'll use to confirm the print came out at the right size.

Print at 100% Scale

Accurate scaling depends entirely on the tag being printed at its exact intended size. When printing:

Set your printer's scaling option to 100%
Do not use "Fit to page," "Shrink to fit," "Scale to fit," or any similar option, as these resize the tag and will produce inaccurate measurements

Verify the Printed Size

Each tag includes a printed measurement scale, for example a line labeled "6 inches." After printing, measure that line with a ruler to confirm it matches the printed label. If the measurement is off, your print settings scaled the page and you'll need to reprint at 100%.

Tip: Check the printed scale every time you print a new batch of tags. Printer defaults often reset to "Fit to page" between jobs.

2Place the Tag in Your Scene

Once printed, how you position the tag matters as much as how you printed it.

Keep the tag flat: Mount it on cardstock, foam board, or a similar rigid backing. A curled, bent, or wrinkled tag distorts the measurement
Use only one tag: Make sure no other tags are visible anywhere in the scene
Position it where you'll photograph it: Place the tag somewhere it will be clearly visible from multiple angles as you move around the subject

3Capture the Tag

Capture your scene as you normally would, making sure the tag is included in your photos:

The tag must appear in at least eight photos
Capture it from several angles rather than repeatedly from the same position
Keep all four corners of the tag within the frame and in focus

Tip: Tag photos count toward your scene coverage, so there's no need to shoot them separately. Just make sure the tag stays in frame as you work your way around the subject.

4Review Your Scaled Capture

Once your capture finishes processing, it will be scaled to real-world dimensions automatically. Measure a known object in your scene to spot-check the result. When the tag is printed at 100%, kept flat, and captured in eight or more photos, dimensional accuracy is typically greater than 99%.

Troubleshooting

My capture wasn't scaled

If your capture came back unscaled, check the following, in order:

More than one tag in the scene: This is the most common cause. Only one tag can be present
Too few photos of the tag: The tag needs to appear in at least eight photos
Tag too small for the scene: Reprint at a larger size and recapture
Corners obscured or out of frame: All four corners need to be visible and in focus

My capture was scaled, but the dimensions are off

This usually points to a printing or mounting issue rather than a capture issue:

Measure the scale printed on your tag with a ruler. If it doesn't match its label, the tag was printed at the wrong size
Check that the tag was flat during capture. A bent or curled tag distorts the reference measurement

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