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Edit LAS file classification codes

Available with 3D Analyst license.

Every lidar point can have a classification assigned to it that defines the type of object that has reflected the laser pulse. Lidar points can be classified into a number of categories, including bare earth or ground, top of canopy, and water. The different classes are defined using numeric integer codes in the LAS files.

Lidar points stored in LAS files are typically classified into different categories using specialized classification tools outside of ArcGIS. This classification is usually completed by setting parameters based on the terrain, and then running algorithms on the point cloud to determine the feature type associated with each point. The classification code assigned to each point is written to the LAS file and, in most cases, adheres to the ASPRS standard.

When a classification is carried out on lidar data, points may fall into more than one category of the classification. Classification flags are used to provide a secondary description or classification for lidar points. In later versions (LAS 1.1 and later), class flags were used to solve this problem. Classification flags were added to the LAS standard to mark points with information additional to the traditional classification. Synthetic, key-point, withheld, and overlap flags can be set for each lidar point. These flags can be set along with the classification codes. For example, a water record could be given a classification code for water (9), as well as a withheld flag. The point will remain in the dataset but will be withheld from any additional analysis on the LAS files.

In many cases, LAS files may not be fully or correctly classified when introduced to the GIS tools in ArcGIS. ArcGIS provides the LAS dataset and associated tools to enable classification or data cleanup of classification codes and classification flags residing in the LAS files.

Interactive and geoprocessing tools provide the ability to edit classification codes present in the LAS file. The Classification tab for a LAS dataset provides interactive editing capabilities as well as automated editing by opening the appropriate geoprocessing tool associated with the analysis.

Follow these steps to access the LAS dataset Classification tab.

  1. Select a LAS dataset layer in the Contents pane.
  2. Click the Classification tab.
  3. Continue to interactively select points to edit, or use the Automated button to list a selection of geoprocessing tools to automate classification editing. A description of each tool is provided in the table below.

Geoprocessing toolsDescription
Classify Ground

Classifies unclassified LAS points into ground points.

Classify LAS Building

Classifies building rooftop points in aerial lidar data.

Classify By Height

Reclassifies lidar points based on their height from the ground surface.

Classify Using Features

Changes lidar classification codes assigned to lidar points based on their proximity to feature data. For example, breaklines representing water boundaries can be used to classify all points within the water boundaries as class code 9 to represent water.

Classify By Proximity

Identifies lidar points within the three-dimensional proximity of z-enabled features while also providing the option to reclassify the points and export them to an output feature class.

Change Class Codes

Modifies the classification codes for LAS files referenced by a LAS dataset. This tool will reclassify one set of classification codes into another, which is particularly useful for updating the classification of LAS files generated prior to the introduction of classification standards in the LAS 1.1 specification. The tool can be used to ensure such data conforms to the current standards.

Note:
  • You cannot save your edits to new LAS files in ArcGIS. You can only edit the classification currently defined in the LAS files referenced by the LAS dataset. All changes are permanent when making any modifications to the classification codes in LAS files. If you are conducting any what-if scenarios or do not want changes to be permanent, make sure to work on a copy of the LAS files and not the originals. You can also use the Extract LAS tool to extract a portion of a LAS file to conduct an initial test.
  • ZLAS files cannot be edited. Consider extracting them to LAS files and re-adding them to a LAS dataset to edit the classification.
  • Once a selection tool has been chosen, the points that are not full resolution will appear with a light-gray symbology.
  • Press and hold C to use the Explore tool while you are using any of the selection tools. You will be able to zoom and pan around the view during a selection.

Interactive LAS point classification

In many cases, LAS files may not be fully or correctly classified when introduced into ArcGIS, and you may want to manually edit the classification of the LAS points. The Classification tab allows you to interactively manipulate the classification conducted on the LAS files of a LAS dataset. You are able to quickly change the class codes and classification flags that are presently set on the selected points.

Follow these steps to interactively edit the classification of the LAS points.

  1. Select a LAS dataset layer in the Contents pane.
  2. Click the Classification tab.
  3. Use the Navigate tool to navigate to the desired location to select LAS points.
  4. Use the Select drop-down menu to choose a selection method. To learn more about selection in ArcGIS Pro, see Select features interactively.
    Note:

    Once a selection tool has been chosen, the points that are not full resolution will appear with a light-gray symbology. Move around the display to change the points that are selectable. Press and hold C to use the Explore tool while you are using any of the selection tools.

  5. Select the desired points.
  6. From the Interactive Edit group, click the Classification Codes drop-down menu to choose the new classification code for the selected points. You may also set or clean classification flags. Select the desired classification flag and choose either Set or Clear from the drop-down menu. The classification codes and classification flags are described below.
  7. Click Apply Changes to commit the edits. All changes are permanent and cannot be undone.
    Note:

    You can always click the Clear button to clear any selected points.

Classification codes and classification flags

The following table contains the LAS classification codes as defined in the LAS 1.4 standard:

Classification value Meaning

0

Never classified

1

Unassigned

2

Ground

3

Low Vegetation

4

Medium Vegetation

5

High Vegetation

6

Building

7

Low Point

8

Reserved

*

9

Water

10

Rail

11

Road Surface

12

Reserved

*

13

Wire - Guard (Shield)

14

Wire - Conductor (Phase)

15

Transmission Tower

16

Wire-Structure Connector (Insulator)

17

Bridge Deck

18

High Noise

19-63

Reserved

64-255

User Definable

The following table describes the classification flags for LAS format 1.1–1.4 that can be set:

Flag nameDescription

Synthetic

A point that was created by other than lidar collection, such as digitized from a photogrammetric stereo model.

Key-point

A point considered to be a model key-point and should not be withheld in any thinning algorithm.

Withheld

The point should not be included in processing.

Overlap

A point that is within the overlap region of two or more flight lines or swaths (LAS version 1.4 specific).