2. Photogrammetry-
The science of quantitative analysis of
measurements from photographs
Photos Gamma Metron
•Photons •To Draw •Metric
•Light •To
Measure
3. Photogrammetry
What’s the primary objective???
• The primary objective of the technique is to
derive precise coordinates of a point.
How this is done???
• This is done by viewing the area from two
different angles, thereby recreating the same
conditions as it existed at the time of
photography.
5. How it is done?
Mathematically intersecting converging
lines in space, the precise
location of the point can be determined.
6. Principals of Photogrammetry
Information needed to determine 3D locations:
1. The location of each camera’s perspective centre.
Exterior
2. The orientation (rotation) of each camera about its perspective centre.
Orientation
3. The location of the point on each image sensor.
This is the essence of photogrammetry!
Image Matching
7. WHY Close Range
PHOTOGRAMMETRY???
• Very precise
• Time effective
• Cost effective
• Based on well established and tested
Algorithms
• Corrects all sorts of distortions
• Wider Scope of Applications
9. Objectives
• Making accurate 3-D models
– Can be used for Accurate Measurements
• Making Textured models
– Can be used as a final product(Photo-Realistic)
• Making Dense Surface Models
– Can be used for Meshing, Contour Maps
10. Methodology
Camera
Calibration
Data
Acquizition
All
Stero
Directional
11. Calibration
• Camera Calibration is the process of
determining the characteristics of a camera so
it can be used as a measurement device.
• Characteristics include
– focal length,
– imaging scale,
– image center and
– lens distortion.
12. The Process…
• Deciding on Camera and the Focal length.
• Taking Photographs
– 12 Photographs of the Calibration Sheet each
from Different Angles (Geometry).
• Importing the Images to Photomodeler Pro.
• Invoking the Automatic Camera Calibration
Process.
14. The Outcome
• Focal length
– The distance between the optical center of the lens and
where the optical axis intersects the image plane.
• Imaging scale
– CCD Format Size
• Principal point
– where the optical axis of the lens intersects the
photograph
• Distortion Parameters
– Radial Distortions
– Decentric Distortions
16. Data Acquisition
Planning the measurement Project
Involves selecting the number and locations of camera
positions for taking the photographs.
17. Data Acquisition
Stero Photography
Camera Axis Unchanged while capturing Photographs
30-60% overlap between two side by side
Photographs
All Directional Photography
Photography from all directions
45% change gives good overlap
18. Data Preparation
1. Feature Marking :
– Involves marking Target Features on Photographs
– Target Features can be formed using
Points, curves, Edges, Cylinders or Shapes.
– Higher level features such as lines and surfaces
are then built on these marked features.
20. Orientation
• Done by Referencing the Photographs
– The points occurring in two are more photographs
are referenced
– Similarly Edges or Curves are also referenced
The Process is same as that of “geo-Referencing”
the satellite image. The Difference here is no
Toposheet or Already Referenced Photograph is
Used.
22. Idealisation
• An ideal camera has
– no lens distortion,
– square pixels, and
– a centered principal point.
• The images in the project are Resampled and
• The photographic marks are shifted to match
the new idealized images.
24. Data Processing
Data
Processing
Point cloud Surface
Meshing Texturing
generation generation
25. • Point Cloud Generation
1. For each pair of photographs, overlap is checked,
a) align the image rows along the epi-polar lines
b) to reduce the image to the region of interest
2. The algorithm searches along a row of the destination image
using an N x N patch of imagery from the source image.
3. Where it finds a good match it records it.
4. All the matches are then optimized for the best overall fit,
throwing out bad and weak matches
5. A sub pixel refinement is carried out for the matches.
6. The matched positions are used to create 3D points using
camera station information.
26. • Meshing
– Equivalent to Triangulated Irregular Network
28. Texturing
• Block Adjustment is the process of defining
the mathematical relationship between the
images contained within a block, the camera
or sensor model, and the ground. Once the
relationship has been defined, accurate
imagery can be created.
29. Exporting the Data
• The Resulting 3D Data can be exported to CAD
or any other Graphics Program for further
application specific processing. Various file
formats are available in Photomodeler Pro like
DXF, 3DS, OBJ, VRML, IGES, 3DM, STL or RAW
files.
Editor's Notes
That’s the beauty of CRP algorithms. You are Locally Defining a Temporary 3 Dimensional Co-ordinate System.
