We wanted to check if the technique "photogrammetry" is suitable for the calculation of surfaces. To do that, we compared Photogrammetry with two other methods. Based on an exposed concrete surface, we wanted to determine the porosity.
By processing multiple images from different perspectives, the program CapturingReality tries to find relationships between the images. Unique overlaps are identified and ranked next to each other. The more images that are detected, the more accurate and dense is the point cloud and so a 3D object can be created.
To calibrate the photos in retrospect a ColorChecker was used.
A measurement on the ColorChecker lets the program derive the actual size of the object.
25% deviation to "white" in the original image
5% deviation to "white" after processing the image with ColorChecker
Pore calculation study:
Calculation of pore area of exposed concrete by photogrammetry in comparison to two alternative measuring methods
Project schedule: For the determination of the pore area using exposed concrete, we compare the calculations of the depth information of a photogrammetric 3D model with two alternative methods on a test area of 50x50 cm.
Method 1: Tracing paper Transparent paper is placed on the concrete surface and the pores are drawn with a pencil. Subsequently, the areas of the points are calculated manually by means of circle and ellipse. (Recording time: approx. 40 min, evaluation duration: approx. 1.5 h)
Method 2: CAD A photo is taken from the surface and implemented in AutoCAD to visually draw polylines and calculate their area. (Recording time: approx. 2 min, evaluation time: approx. 3 h)
Method 3: Photogrammetry With the help of photos from various perspectives, a detailed 3D object is created by photogrammetry. The depth information of this model determines the pores of the surface. (Recording time: approx. 40 min, 3D reconstruction: approx. 9 h; required computing power, evaluation time: immediately)
|photo and CAD||tracing paper||photogrammetry|
|area pores||17.45 cm2||19 cm2||4.93 cm2|
|area frame||2500 cm2||2500 cm2||2500 cm2|
|proportion of pores||0.70 %||0.76 %||0.20 %|
Proportion of pores:
Method 1: Tracing paper
- least time with 2.17 h
- largest pore area ratio calculated with 19 cm2
Method 2: CAD
- a lot of time with 3.03h
- similar pore area fraction as method 1 with 17.47 cm2
Method 3: Photogrammetry
- high time expenditure with 2h working time and 9h needed computing power
- lower pore area content with 4.93 cm2