Reliability of reference distances used in photogrammetry
Muge Aksu1, Demet Kaya, Ilken Kocadereli
1Department of Orthodontics, Hacettepe University Faculty of Dentistry, Hacettepe University, Ankara, Turkey. mugepeh@hacettepe.edu.tr
The Angle Orthodontist
|May 21, 2010
Summary
Photogrammetric assessment reliability varies. The T-Ex reference distance is reliable for profile measurements (Prn-Sn, Sn-Sto), while Ex-Ex and En-En are reliable for frontal measurements (Ch-Ch) in males.
Area of Science:
- Medical Imaging
- Anthropometry
- Facial Analysis
Background:
- Photogrammetry is increasingly used for facial analysis.
- Establishing reliable reference distances is crucial for accurate photogrammetric measurements.
- Previous studies have shown variability in the reliability of different facial landmarks.
Purpose of the Study:
- To evaluate the reliability of specific reference distances used in photogrammetric facial assessments.
- To compare direct facial measurements with indirect measurements from standardized photographs.
- To determine the accuracy of photogrammetric methods for various facial parameters.
Main Methods:
- 100 subjects underwent direct facial measurements of five lateral and four frontal parameters.
- Standardized photographs were taken for indirect photogrammetric measurements.
- Reliability was assessed using repeated measures ANOVA and Bland-Altman analyses, comparing direct and indirect values.
Main Results:
- Profile measurements: T-Ex reference distance showed reliability for Prn-Sn and Sn-Sto in both sexes. Sa-Sba was less reliable for N-Sn (females) and Sn-Me (males).
- Frontal measurements: Ex-Ex and En-En reference distances were reliable for Ch-Ch in males. P-P reference distance yielded poorer results.
- Statistical differences between direct and indirect values were noted for most parameters, with exceptions depending on the reference distance and sex.
Conclusions:
- The T-Ex reference distance is reliable for specific profile measurements (Prn-Sn, Sn-Sto) in both sexes.
- Ex-Ex and En-En reference distances are reliable for frontal Ch-Ch measurements in males.
- Photogrammetric reliability is parameter and reference distance-dependent, necessitating careful selection for accurate facial analysis.
Related Concept Videos
01:26Influence of Earth's Curvature and Atmospheric Refraction on Leveling
During leveling, the Earth's curvature and atmospheric refraction introduce deviations in the line of sight from a true horizontal reference. When the line of sight is leveled, it remains perpendicular to the plumb line only at a single point. Beyond this, it deviates due to the Earth’s curvature, represented by the correction C. For a sight distance D, the deviation can be derived using the relationship:This relationship shows that the deviation increases quadratically with distance. Over a...
01:15Distance Corrections
To achieve precise distance measurements, especially in surveying and construction, certain corrections must be applied to account for potential sources of error like the standardization errors, temperature variations, and slope adjustments.Standardization error emerges when measurement equipment undergoes changes, such as wear, repairs, or weather impacts. To address this, surveyors compare the equipment’s readings to a standard. This process identifies any deviation that might lead to...
01:17Common Leveling Mistakes and Errors
A survey team is tasked with determining the elevation difference between points Point A and Point B, separated by uneven terrain. They use a leveling instrument and a leveling rod.Common MistakesMisreading the Rod: During a backsight reading at Point A, the instrumentman observes the rod partially obscured by tall grass. Instead of reading 1.135 m, they mistakenly record 1.735 m due to the misalignment of the crosshair with the wrong graduation. This error adds 0.600 m to all subsequent...
01:10Design Example: Measuring Distance Between Two Points with Obstructions
When measuring distances in areas with physical obstructions, such as a lake in a field, surveyors must employ techniques to calculate accurate lengths without direct line measurements. One effective method is the offset technique, which allows for precise distance estimation over inaccessible stretches.In this scenario, a surveyor must measure a side of an area that crosses a lake. Since the measuring tape cannot span the lake, the surveyor begins by establishing a baseline that aligns with...
01:30Types of Global Positioning System Surveys
GPS surveying methods vary in application, accuracy, and data collection techniques, catering to diverse surveying and mapping needs. Static GPS, kinematic GPS, and real-time kinematic (RTK) surveying are widely used. Each technique offers distinct advantages.Static GPS involves placing one receiver at a known reference point and another at the target point. It collects exact positional data by observing multiple satellite ranges over an extended period, achieving centimeter-level accuracy for...
01:20The Distance Formula
In geometry, measuring the direct distance between two points on a plane is essential in various practical and theoretical applications. Whether in navigation, engineering, or computer graphics, determining the shortest path between two locations involves using the distance formula. This formula is derived from the Pythagorean Theorem, which relates the lengths of the sides of a right triangle. On a coordinate plane, the horizontal and vertical distances between two points serve as the legs of...