derived point clouds - knowledge...
TRANSCRIPT
21-Jun-17
1
Photogrammetric Point Cloud Processing
Jim Maloney
GeoCue Group, Inc.
9668 Madison Blvd., Suite 202
Madison, AL 35758
+1 (256) 461-8289
support.geocue.com
GeoCue Terrasolid LIDAR TrainingTerrasolid Training Webinar – 22 Jun 2017
Derived Point Clouds
• Noisy Data
• Very Dense- 200-500 pts/m2.
• Lack of points below Vegetation
05-07 Jun 2017 GeoCue/Terrasolid Training – Mercer 2
21-Jun-17
2
Pre-Processing Macro
• Echo information and surface roughness are not as useful with ground
classification with photogrammetric point clouds, we need to take a
different approach to deal with the noise than we do with normal
LIDAR data
05-07 Jun 2017 GeoCue/Terrasolid Training – Mercer 3
Classify Isolated Points
• Isolated points within a photogrammetric point cloud are never useable
and almost always not meaningful.
05-07 Jun 2017 GeoCue/Terrasolid Training – Mercer 4
21-Jun-17
3
Classify Surface
• Classifies suitable points into a Potential surface class for further
examination by identifying the median points within this noisy surface.
05-07 Jun 2017 GeoCue/Terrasolid Training – Mercer 5
Smoothen XYZ
• Modifies the XYZ positions of the Model Keypoints to produce a more homogenous representation of surfaces, both horizontal and vertical.
05-07 Jun 2017 GeoCue/Terrasolid Training – Mercer 6
Surface Points
Smoothed Surface Points
21-Jun-17
4
Thin Points
• Reduces the density of the points to make the dataset more
manageable.
05-07 Jun 2017 GeoCue/Terrasolid Training – Mercer 7
Raw Point Cloud
Processed Point Cloud
Classify Hard Surface
• Classifies tentative ground in a similar manner as the Classify Surface
routine. It classifies points on a plane-of-best-fit within a tolerance
05-07 Jun 2017 GeoCue/Terrasolid Training – Mercer 8
21-Jun-17
5
Classify Ground
• Classifies the final ground class in preparation for above ground
feature classification processing
05-07 Jun 2017 GeoCue/Terrasolid Training – Mercer 9
Photogrammetric Point Cloud Workflow• Pre-Processing and data review
• Classify Isolated Points
• Classify Potential Surface (Surface Routine)
• Smoothen Potential Surface
• Thin Potential Surface
• Classify Tentative Surface (Hard Surface Routine)
• Classify Ground (Ground Routine)
17-21 Apr 2017 GeoCue/Terrasolid Training – Mercer 11
21-Jun-17
6
Classification Using Groups
• Run grouping of above ground
points
• Goal is to have each object as one
group of points
• Software stores group value for
each point in FastBinary file format
• Manual and automatic classification
can work on object level
05-07 Jun 2017 GeoCue/Terrasolid Training – Mercer 12
Group Classification Macro
05-07 Jun 2017 GeoCue/Terrasolid Training – Mercer 13
21-Jun-17
7
Compute Distance
• Computes the distance between points and the ground.
• This distance information is stored for use in other routines.
05-07 Jun 2017 GeoCue/Terrasolid Training – Mercer 14
Classify by Distance
• Classifies points into medium and high vegetation based on the
distance values computed in the previous step.
05-07 Jun 2017 GeoCue/Terrasolid Training – Mercer 15
21-Jun-17
8
Assign Groups
• Builds groups from points in source classes
• Typically high vegetation or medium+high vegetation
• Can use four different grouping principles:
• Group planar surfaces finds large enough planar surfaces such as
roofs or walls
• Group by tree logic finds groups using watershed algorithm starting
from highest local point
• Group by density uses spacing between points
05-07 Jun 2017 GeoCue/Terrasolid Training – Mercer 16
Classify Groups / By best match
• Software can evaluate each group using multiple object recognition
routines
• Classifies each group to best matching class
Example: software may evaluate one group to be:
• Building roof with 0% probability
• Building wall with 0% probability
• Tree with 77% probability
• Pole with 42% probability
• Vegetation with 58% probability
• Car with 0% probability
05-07 Jun 2017 GeoCue/Terrasolid Training – Mercer 17
21-Jun-17
9
Processing Steps for Airborne LIDAR
• Classify ground
• Classify wires if needed
• Use compute distance to compute height above ground value for each point
• Classify medium vegetation using 'Classify / By distance'
• Classify high vegetation using 'Classify / By distance'
• Group points using 'Group / Assign groups'
• Classify groups using 'Group / Classify / By best match' and other group based
routines
05-07 Jun 2017 GeoCue/Terrasolid Training – Mercer 18
Exercise #1800
05-07 Jun 2017 GeoCue/Terrasolid Training – Mercer 19
Complete the following exercise using the training set data (or your own data).
Please refer to handout for full details:
1. Load (or reload) the laser points from your GeoCue Sample Project.
2. Classify Isolated Points
3. Classify Surface
4. Smoothen XYZ
5. Thin Points
6. Classify Hard Surface
7. Classify Ground.
8. Compute distance
9. Classify by Distance
10. Assign Groups
11. Classify by Best Match