1.5 Measuring and Comparison 3D 17
1.5 Measuring and Comparison 3D
For measuring in 3D, the following approaches are available:
• The approaches used for measuring and comparison 2D (see page 16) in combination with a camera cali-
bration (see Solution Guide III-C, section 3.2 on page 59) for measuring objects that are viewed by a single
camera and that lie in a single plane.
• Pose estimation (Solution Guide III-C, chapter 4 on page 89) for the estimation of the poses of 3D objects
that are viewed by a single camera and for which knowledge about their 3D model (e.g., known points,
known circular or rectangular shape) is available.
3D reconstruction is an important subcategory of 3D measuring and comprises the following methods:
• Stereo for measuring in images obtained by a binocular or multi-view stereo system on page 239. Further
information can be found in the Solution Guide III-C, chapter 5 on page 115.
• Laser triangulation using the sheet-of-light technique (Solution Guide III-C, chapter 6 on page 145) for
measuring height profiles of an object by triangulating the camera view with a projected light line.
• Depth from focus (Solution Guide III-C, chapter 7 on page 161) for getting depth information from a se-
quence of images of the same object but with different focus positions.
• Photometric Stereo (Reference Manual, chapter “3D Reconstruction . Photometric Stereo”) for getting
information about an object’s shape because of its shading behavior (e.g., by the operator photomet-
ric_stereo).
1.6 Object Recognition 2D
For finding specific objects in images, various methods are available. Common approaches comprise:
• Blob Analysis on page 35 for objects that are represented by regions of similar gray value, color, or texture.
• Contour Processing on page 85 for objects that are represented by clear-cut edges. The contours can be
obtained by different means:
– Edge Filtering on page 59 if pixel precision is sufficient.
– Edge and Line Extraction on page 67 if subpixel precision is needed.
• Matching on page 97 for objects that can be represented by a template. Matching comprises different ap-
proaches. For detailed information about matching see the Solution Guide II-B.
• Classification on page 143 for the recognition of objects by a classification using, e.g., Gaussian mixture
models, neural nets, or support vector machines. For more detailed information about classification see the
Solution Guide II-D.
• Color Processing on page 157 for the recognition of objects that can be separated from the background by
their color.
• Texture Analysis on page 171 for the recognition of objects that can be separated from the background by
their specific texture.
• Movement detection (see section 1.13 on page 19) for the recognition of moving objects.
1.7 Object Recognition 3D
For the recognition of 3D objects that are described by a 3D Computer Aided Design (CAD) model, see the
descriptions for 3D Matching on page 121. For the recognition of planar objects that can be oriented arbitrarily
in the 3D space, see the descriptions for perspective, deformable matching and descriptor-based matching in the
chapter about Matching on page 97 for the uncalibrated case and in the Solution Guide III-C, chapter 4 on page 89
for the calibrated case.
Guide to Methods