Side-view measurement
Gonial angle: what a side photo measures.
The opening at the jaw corner is one geometric feature. It is not a complete measure of jaw definition, and a photograph does not reveal the joint inside.
In a skeletal analysis, the gonial angle describes the relationship between the ascending and lower parts of the mandible. The chosen lines depend on the measurement method. For example, a radiographic study measured tangents along the rear and lower bony borders. See the radiographic method.
TrueMax does something more limited: it measures the angle between three points placed on a side photograph. The label is familiar, but the endpoints are visible surface landmarks, including an estimated hinge location. The result is not the skeletal angle from an X-ray.
- A
- Jaw hinge estimate, on the skin in front of the upper ear flap.
- B
- Visible jaw corner. The angle opens here.
- C
- Chin bottom, not chin front.
- E
- Ear notch. Separate from the hinge estimate.
Which three points should you review?
- Jaw corner: the visible turn where the lower jaw outline rises toward the ear. This is the vertex of the angle, not a point halfway along the cheek.
- Jaw hinge estimate: skin just in front of the upper part of the small ear flap. Do not move it to the sideburn or cheekbone to make the line look stronger. The exact joint cannot be located from the photograph.
- Chin bottom: the lowest point of the visible chin. This is different from the chin-front point, which is the furthest-forward part of its outline.
The nearby ear notch marks the notch at the top of the ear flap. It can sit close to the hinge estimate, but the two points have different jobs. TrueMax does not use the ear notch as a substitute for the hinge estimate in this angle.
Why moving a point changes the answer
The angle comes from the direction of the two rays at the jaw corner. Moving the hinge estimate changes the upper ray. Moving the chin-bottom point changes the lower ray. Moving the jaw corner changes both. A cleaner-looking outline is not evidence of a more accurate placement.
A pair of rays drawn 120 degrees apart measures 120 degrees, regardless of whether the image is enlarged uniformly. That is a geometry check, not an ideal value or proof that a detector found the correct anatomical points. Turning the head, stretching the image or moving a landmark is a different change.
Why a sharper-looking jaw can have a similar angle
This construction uses three positions. It does not measure the skin, fullness, shadow, facial hair or the visibility of the jaw boundary between them. Two photographs can share a similar angle while their jaw outlines look very different. A favourable model reading does not establish low facial fat, and this scan does not give a body-fat percentage.
The reference remains provisional
TrueMax's current gonial scoring reference was borrowed from skeletal measurements and has not been validated for these photographic surface points. A model range is not a universal ideal. A score should not be used to diagnose a jaw problem or decide on a procedure.
How to compare another app's result
Check the same photo, the exact vertex, both ray endpoints and whether the result is a surface angle or a skeletal construction. Matching names or units alone is not enough. One study compared specific landmarks from 3D laser scans and CT; its findings do not validate a different 2D phone-photo method. Read the 3D measurement study.
If a point is hidden by hair or the face is not fully side-on, retake the photo or leave the side result out. Reviewing a point is useful, but does not make an obscured landmark knowable.
Check the points before the score
Use the capture guide, then review the placements. Continue with what a side-profile analysis includes or the scoring methodology.
Start a face scan