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Placing the markers

Good marker placement matters more than any detector setting. On the Bogong moth, hinges placed 20 px from the wing bases doubled the noise in L − R, and a sector that clipped the body caused large L − R spikes. This page explains what each marker means, so you can place them right the first time.

Sector geometry A tethered insect seen from above with its head up. Each wing has an annular sector centred on its hinge, from the inner radius just past the body to the outer radius inside the wing blur. The leading edge of the blur, on the head side, is the reported wing angle, measured from the perpendicular to the body axis and positive toward the head. +φ head tail body axis leading edge 0° perpendicular to the body inner radius just past the body outer radius inside the blur hinge stroke envelope (motion blur) sector start → start + span left wing right wing

The body axis: head and tail

Drag the magenta dot onto the head and the cyan dot onto the tail (the tip of the abdomen). The line between them is the body axis. Every wing angle is measured relative to it, so it does not matter how the insect is rotated in the image. Put the dots on the midline, as far apart as the insect allows: a longer axis is a more precise one.

The wing hinges

The red (left) and green (right) dots are the wing hinges: the points each wing turns about, at its base. The sector is drawn around the hinge, and every edge angle is measured from it.

A hinge in the wrong place does not make the trace look wrong, it makes it biased: if the hinge sits away from the true pivot, the edge you measure moves in angle as the wing sweeps, and the error changes with the stroke. To find the true hinge, watch the leading edge across several frames. Straight lines along it all pass through one point, and that point is the hinge. (For the Bogong moth example, lines fitted to 190 frames of one wing passed within 0.7 px of one point; see The Bogong moth example.)

While Asymmetric is off, the wings mirror each other across the body axis: drag one hinge and the other follows. Turn it on for insects that sit at an angle or rigs where the two wings look different.

The sectors

Each wing is tracked inside an annular sector: a ring segment around its hinge, bounded by two radii and two angles.

SettingWhat to aim for
Inner radius (inner_radius)Just past the body. Closer in, the hinge region and the thorax edge dominate the profile, and every angle bin covers only a few pixels
Outer radius (outer_radius)Inside the wing blur. Beyond the blur there is only background and noise; a little short of the wing tip is ideal
Start and span (start_deg, span_deg)Cover the whole stroke, from the most backward to the most forward position, with a few degrees of margin. Stay clear of the body, the head, the legs and the antennae

To edit, drag the corner dots (angle and outer radius at once), the middle dot of an arc (only that radius), or the white centre dot (the whole setup). Precise values can be typed in Settings.

Sector angles in the config are image angles: degrees clockwise from image-right, as the image’s y axis points down. You rarely need to type them; drag instead.

What gets measured

Inside the sector, Rekkefly averages the image along each ray from the hinge and builds an angular profile: brightness against angle. The blurred wing is a broad plateau in that profile. Its edge toward the head is the leading edge, and its angle is the wing angle:

  • 0° is the outward perpendicular to the body axis (the dashed line);
  • angles are positive toward the head, negative toward the tail;
  • L − R is the left angle minus the right angle; L + R is their sum.

These are Kinefly’s conventions, so values compare directly with Kinefly data. How the edge is found, and how legs and antennae are ignored, is described in The detectors.

Head and abdomen

Two more sectors track the head and the abdomen (toolbar H and A; off by default). Their hinge is the pivot (the neck, or the petiole), and the sector should cover the part’s range of motion. They use the intensity centroid rather than an edge, and report an angle along the body axis, clockwise positive in the image.

A checklist

  1. The head and tail dots are on the midline.
  2. Each hinge is on the wing base, where the leading edges meet.
  3. The inner radius is just past the body: no part of the thorax inside the sector.
  4. The outer radius ends inside the wing blur.
  5. The sectors cover the full stroke, plus a few degrees, and miss the legs and antennae.
  6. With Settings → Show signal diagnostics, L − R is smooth while the insect flies.

Agents can do the same check: the MCP snapshot tool returns the frame with the sectors and edges drawn on it (AI agents).