Reliability of reference distances used in photogrammetry

Abstract

Objective: To determine the reliability of the reference distances used for photogrammetric assessment.

Materials and methods: The sample consisted of 100 subjects with mean ages of 22.97 +/- 2.98 years. Five lateral and four frontal parameters were measured directly on the subjects' faces. For photogrammetric assessment, two reference distances for the profile view and three reference distances for the frontal view were established. Standardized photographs were taken and all the parameters that had been measured directly on the face were measured on the photographs. The reliability of the reference distances was checked by comparing direct and indirect values of the parameters obtained from the subjects' faces and photographs. Repeated measure analysis of variance (ANOVA) and Bland-Altman analyses were used for statistical assessment.

Results: For profile measurements, the indirect values measured were statistically different from the direct values except for Sn-Sto in male subjects and Prn-Sn and Sn-Sto in female subjects. The indirect values of Prn-Sn and Sn-Sto were reliable in both sexes. The poorest results were obtained in the indirect values of the N-Sn parameter for female subjects and the Sn-Me parameter for male subjects according to the Sa-Sba reference distance. For frontal measurements, the indirect values were statistically different from the direct values in both sexes except for one in male subjects. The indirect values measured were not statistically different from the direct values for Go-Go. The indirect values of Ch-Ch were reliable in male subjects. The poorest results were obtained according to the P-P reference distance.

Conclusions: For profile assessment, the T-Ex reference distance was reliable for Prn-Sn and Sn-Sto in both sexes. For frontal assessment, Ex-Ex and En-En reference distances were reliable for Ch-Ch in male subjects.

Figure 1

Soft tissue parameters measured on the profile view: T-Ex (tragus-exocanthion) tragus-exocanthion distance, Sa-Sba (superaurale-subaurale) ear length, Tri-N (trichion-nasion) superior facial third, N-Sn (nasion-subnasale) nose height or middle facial third, N-Prn (nasion-pronasale) nasal bridge length, Prn-Sn (pronasale-subnasale) nasal tip protrusion, Sn-Sto (subnasale-stomion) upper lip height, and Sn-Me (subnasale-menton) inferior facial third.

Figure 2

Soft tissue parameters measured on the frontal view: Ex-Ex (right exocanthion-left exocanthion) biocular width, En-En (right endocanthion-left endocanthion) intercanthal width, P-P (midpoint of right pupil-midpoint of left pupil) interpupillary width, Al-Al (right alare-left alare) alar width, Ch-Ch (right cheilion-left cheilion) mouth width, Go-Go (right gonion-left gonion) gonial width, and Sn-Sto (subnasale-stomion) upper lip height.