Measuring Rules & Guidelines

Accurate fish measurement is essential for fair competition, conservation, and data integrity. SnapCatch uses AI to verify each submission - but it starts with you, the angler, getting the photo right.

How to Measure a Fish on the SnapCatch Measure Mat

Step-by-Step Guide

1

Use the official SnapCatch measure mat

Only SnapCatch-branded mats are accepted to ensure consistency and accuracy. The mat may not be modified in any way that affects the ability to measure the fish accurately from the jaw tip.

2

Lay the fish flat and side-on

Place your fish side-on on the mat with either the upper or lower jaw touching the L-shaped plastic end (zero marker). This edge ensures consistent placement for accurate AI validation.

3

Head to zero

The fish’s snout must be firmly touching the “0 cm” marker. The mouth can be open or closed, but the nose must make contact with the end stop.

4

Tail positioning

Ensure the V of the tail is clearly visible and positioned as close to the midline of the measure as possible.

5

Take a clear photo – directly from above

  • Use the SnapCatch app and its in-app camera.
  • Take the photo directly above the fish (looking straight down), not from the front or side.
  • The entire fish must be visible from snout to tail, with the measurement markings clear and readable.

6

No manipulation

Do not stretch, squeeze, or alter the fish to influence length. Do not edit, crop, or digitally modify the image in any way.

7

Respect the catch

Once measured, either release the fish safely or fully utilise it if you are keeping it, in line with NZOFC values.

Important

A clear photograph of the fish, correctly placed on the measure, is critical for your entry into the competition. It is your responsibility to ensure you provide an image that the AI can confidently use to validate your entry. Submissions that don’t meet these standards may be rejected without notice.

‍What Will Be Rejected
  • Fish not aligned correctly (snout not at 0 cm)
  • Any part of the fish not visible in the frame
  • Blurry, shadowed, or obstructed images
  • Use of non-official SnapCatch mats
  • Photos taken at an angle or with measurement lines obscured
  • Signs of tampering or misrepresentation
  • Use of modified or damaged mats
  • Fish covered in excessive blood, sand, mud, or any other obstruction that interferes with accurate identification

‍

Disclaimer

‍While every care is taken with the production of SnapCatch measure mats, NZOFC and SnapCatch take no responsibility whatsoever in the use of this measure for the purposes of determining the legal length of any fish caught. The measure should be calibrated from time to time with another accurate measuring device.

‍

Tips for Best Results
  • Use natural light whenever possible
  • Clean your lens before taking the photo
  • Avoid shadows or hands covering any part of the fish
  • Ensure the entire fish and measurement scale are visible
  • Always double-check snout placement before submitting your entry

‍

How SnapCatch Uses ArUco Codes to Measure Your Fish

What Are ArUco Codes?

‍ArUco codes are small, square black-and-white patterns that function like QR codes — but instead of linking to a URL, they help our AI system understand scale, orientation, and distance in a photograph.

These codes are printed directly on every SnapCatch measure mat and are critical to ensuring that the app can accurately measure your catch.

Why We Use ArUco Codes

‍In a photo, it’s difficult to judge size without a known reference. Different camera angles, lighting, or phone types can distort perspective. ArUco codes give our system a precise and consistent reference point so we can calculate fish length accurately - down to the centimetre.

How It Works

  1. Photo Taken in-App
    You take a photo of your fish on the official SnapCatch mat using the app’s camera tool. The ArUco codes are visible in the corners of the mat and in the measuring scale area.
  2. AI Detects ArUco Codes
    SnapCatch’s computer vision system immediately scans the image for the codes. These codes provide a known scale and grid reference, correcting for angle, tilt, and distance.
  3. Length Is Calculated
    Once the system identifies the snout and tail tips of the fish and knows the exact scale from the ArUco codes, it calculates the true length of the fish. This process ensures consistency across all submissions, no matter what device or camera was used.

Why It Matters

  • Fairness: Everyone is measured using the same scale
  • Accuracy: ArUco codes eliminate guesswork
  • Trust: Results can be verified, validated, and stand up to scrutiny in competition

‍

Important for Users
  • Always use the official SnapCatch mat
  • Ensure the ArUco codes are fully visible in your photo
  • Do not cover, damage, or modify the codes
  • Keep the mat clean to ensure reliable code detection

‍

Troubleshooting / Tip

  • Ensure the end of the measure mat does not fold back onto the flat section, as this can cause the ArUco codes to become misaligned. The codes must remain evenly spaced and properly lined up, as any distortion or overlap may interfere with accurate detection and confuse the reading.