Point cloud classifiation including Powerlines with Laserdata LIS Software

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ALS Power Line Classification Tutorial

Content

- data import

- ground classification

- building classification

- vegetation classification

- power line classification

© 2017 LASERDATA GmbHAuthor: Volker Wichmann

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The Data Set

The data set is delivered as compressed ASPRS LAS file (*.laz) with basic attributes like gps-time, return number and intensity. This tutorial describes the processing required to classify the points into the following classes:

- undefined- ground- vegetation (low/mid/high)- building- power line

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Import and Visualization of the Point Cloud

First of all, we import the data set with the following tool:

Tools > LASERDATA LiS > Import/Export > Import LAS/LAZ Files

Provide the data_heli.laz file as input.

Then check those attributes you like to import.

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Import and Visualize Point Cloud

A double left-click on the dataset in the Data tab opens up a Map View:

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3D Visualization

Let's have a quick look at the data set in 3D. We can use the Point Cloud Viewer for this purpose:

Tools > LASERDATA LiS > Visualization > Point Cloud Viewer [interactive]

Provide the point cloud as input.

Also provide the “intensity” attribute with the Intensity parameter.

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3D Visualization

Press shortcut key “2” to change from elevation to intensity colored (use shortcut key “1” to switch back to elevation). We can use this shortcut because we specified the intensity attribute in the parameter settings. Finally quit the Point Cloud Viewer by closing its window.

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Ground Classification

The first step in point cloud classification is to separate the points into ground and non-ground points.

Tools > LASERDATA LiS > Classification > Ground Classification (PC)

Provide the point cloud as input.

Some parts of the terrain are quite steep, so we adjust the Maximum Angle to 30°

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3D Visualization

Let's have a look at the ground classification result in 3D:


The tool remembers the last setting, so we only have to provide the new “grdclass” attribute with the Classification parameter.

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3D Visualization

Press shortcut key “5” to change from elevation to classification colored (use shortcut key “1” to switch back to elevation; use shortcut key “6” to show only ground points). We can use this shortcut because we specified the classification attribute in the parameter settings. Finally quit the Point Cloud Viewer by closing its window.

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Point Cloud Segmentation

Next, as a prerequisite to building classification, we do a segmentation of the non-ground points into planar objects.

Tools > LASERDATA LiS > Segmentation > Segmentation by Plane Growing (PC)

Provide the point cloud as input. We use the ground classification as threshold attribute (so we only segmentize non-ground points)

We need to adjust some parameters: we can use stricter settings as this is a helicopter data set with a higher point density

We only process point class 1 (undefined)

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3D Visualization

Let's have a look at the segmentation result in 3D:


Provide the new “segmentid” attribute with the Random parameter. This allows us to colorize the segments by random.

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3D Visualization

Press shortcut key “q” to change from elevation to random colored (press “q” again to assign another set of random colors). Values of -1 indicate that the point was skipped during segmentation, points skipped in region growing have a segment ID of 0. The individual segments group points on planar surfaces.

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Building and Vegetation Classification

Next, we classify building and vegetation points.

Tools > LASERDATA LiS > Classification > Enhanced Point Cloud Classification

Provide the point cloud as input. We build upon already derived attributes: segmentid, ground classification, and the height above ground

Again we need to adjust some parameters due to the higher point density

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3D Visualization

Let's have a look at the building and vegetation classification result in 3D:


Change the attribute provided with the Classification parameter from “grdclass” to “classid”.

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3D Visualization

Press shortcut key “5” to change from elevation to classification colored; use shortcut key “1” to switch back to elevation; use shortcut keys “6, 7, 8, 9, 0” to change to further visualization options.

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Building Refinement

As you may have noticed, there are some points on building roofs still classified as vegetation. We will clean this up using a majority filter, which is constrained to work only on building and vegetation points.

Tools > LASERDATA LiS > Filtering > Majority Filter (PC)

Provide the point cloud as input and select “classid” as attribute to filter.

Adjust the radius, constrain the filtering to high vegetation points (classid 5), and exclude undefined, ground and lower vegetation points from the computation.

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3D Visualization

Let's have a look at the refined building classification in 3D:


Change the attribute provided with the Classification parameter from “classid” to “majority_classid”.

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3D Visualization

Press shortcut key “5” to change from elevation to classification colored. You can change to the raw classification by changing the Color Attribute from “majority_classid” to “classid”.

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Power Line Classification

Next step is a preliminary power line classification.

Tools > LASERDATA LiS > Classification > Power Line Classification

Provide the point cloud as input and select “majority_classid” with the Classification parameter and “dz” with the Threshold Attribute parameter. We will use the latter to constrain the classification to points higher than 2.5 m.

Also adjust the Search Radius parameter used for line detection to 1.5 m.

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3D Visualization

Let's have a look at the preliminary power line classification result in 3D:


Change the attribute provided with the Classification parameter from “majority_classid” to “classid_pl”.

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3D Visualization

Press shortcut key “5” to change from elevation to classification colored.

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Power Line Refinement

As you may have noticed, some points in vegetation and on building facades are detected as power line. We will clean this up using a refinement filter, which also adds a cable ID to each power line. The latter can be used for catenary curve fitting for example.

Tools > LASERDATA LiS > Classification > Power Line Refinement

Provide the point cloud as input and select the “classid_pl” and “dz” attributes.

Adjust the search radii and the line tolerance.

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3D Visualization

Let's have a look at the refined power line classification in 3D:


Change the Classification parameter to “classid_pl_refined” and the Random parameter to “cableid_pl_refined”.

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3D Visualization


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3D Visualization

Press shortcut key “q” to change to random colored, showing the cable ID (press “q” again to assign another set of random colors).

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Final Classification

As as last step, we will clean up the building facades by labeling all vegetation points (classid 3 to 5) to undefined (classid 1).

Tools > LASERDATA LiS > Classification > Clean Building Facades (PC)

Provide the point cloud as input and select the “classid_pl_refined”

Adjust the search radius and set the Target Class to 1.

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3D Visualization

Let's have a look at the final classification result in 3D:


Change the Classification parameter to “classid_pl_refined_final”

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3D Visualization
