The Control Points Tab has multiple tools to measure and compare an LAS point cloud to control or check points.

Figure 1: Control Points Tab

Control

Import Control Points

Accuracy Star Measurement Utility

Accuracy Analysis

Control Points:	Control Points Layer	Active LAS Layer:	Active LAS Layer		Accuracy Estimation
Elevation Field:	Elevation Field	Drive Mode:	Drive Mode		Apply Correction

Navigation

Results

Control

Import Control Points

The Import Control Points Wizard utilizes the Import from ASCII XYZ tool in a restricted mode to provide a flexible way to define the necessary settings for converting ASCII text files to Feature Files suitable for use as control or check points in the Control Points Report dialog. The Import Control Points Wizard can support many different formats of ASCII files containing LIDAR points. With few exceptions, no preparation should be required to import the text files in their original state.

Control Point Feature Files

In configuring a set of control points or check points for use in the Control Points Tab it is best to follow the convention below to make the most use of the Drive Mode shortcuts available within the toolbar for navigation and filtering. The fields either need to exist in the shapefile or may come from an ASCII file that is then converted to a shapefile using the Import ASCII functionality within LP360.

Desc - Description of the point, as it is entered in the ASCII file.

FID - The full unique ID of the point

Name - The name the point is given in the ASCII file.

Type - The point's type, according to the following convention. Note: Type is case sensitive prior to v2024.1.17.0.

• • FC - Full control point - X, Y, and Z
  • HC - Horizontal aspect of the control point - only X and Y
  • VC - Vertical aspect of the control point - only Z
  • FK - Full check point - X, Y, and Z
  • HK - Horizontal aspect of the check point - only X and Y
  • VK - Vertical aspect of the check point - only Z

The following types were introduced in v2023.1 for the Accuracy Star workflow:

• • AS - Accuracy Star
  • SN - Survey Nail
  • ST - SmartTarget
  • CB - Checkerboard (Auto-Find in v2023.2)
  • CV - Chevron

The following type was introduced in v2023.3:

• • CO - Concentric Circle (Auto-Find in v2023.3)

HOffset - The height of the instrument at the measured position above the control point. Used with Accuracy Stars or Smart Targets that are placed horizontally on the point but sit some distance above it. 

Accuracy X - is the X error of the survey of the control points based on the survey method used to create the point, and as defined by the ASPRS Positional Accuracy Standards for Digital Geospatial Data.

Accuracy Y - is the Y error of the survey of the control points based on the survey method used to create the point, and as defined by the ASPRS Positional Accuracy Standards for Digital Geospatial Data.

Accuracy Z - is the Z error of the survey of the control points based on the survey method used to create the point, and as defined by the ASPRS Positional Accuracy Standards for Digital Geospatial Data.

How to Import Control Points?

For details, see the Import Control Points Wizard.

Accuracy Star Measurement Utility

The Accuracy Star Measurement Utility is a quick tool to calculate the Height offset from the slant distance. This height offset is later used in the Accuracy Estimation tool.

Accuracy Analysis

The Control Points Panels are a series of tools that allows the user to select the type of Control Point file to use, LAS and the tools to navigate between.

Figure 3: Control Points Panel

Control Points Layer

Any point feature class that has an accompanying elevation value can be used as a source of control points. The point features within the selected point feature class are displayed in the profile window for a profile intersecting the points and are used in creating a control point report.

To select the Control Points Layer:

1. Select the arrow next to the Control Points list on the Control Points tab.

2. Select the point feature class you wish to use as a source of control points. Select None if you do not want to use control points.

Tip
If no layers are displayed in the list, add at least one point feature class to the active map or data frame.

Elevation Field

The elevation field defines the source of z values for each control point from the selected control point layer. The elevation values for each point are used to display the control points in the profile window for intersecting profiles and for producing the control point reports. To select the Elevation Field:

1. Select the down arrow on the box.

2. Select the field that will serve as a source of elevation values for each point.

Figure 4: Elevation Field

Tip

The "Shape" field name will appear in the list only if the point feature class supports Z measures.

Active LAS Layer

Active LAS layer is the LAS to be used to measure the control points.

Drive Mode

The Control Point Drive Mode determines which points, check points or control points the panning controls will jump to each time you click them.

Figure 5: Drive Mode

1. On the Control Points toolbar, click the arrow to the right of the Drive Mode list.
2. Select Check or Control to designate which points the panning tools will jump to.
3. Use any of the panning tools: First, Previous, Next, or Last on the Control Points tab to pan to the selected point type.

Tip

Use the Labels command to display textual data that will identify each point on the map display using an available data field.

Accuracy Estimation

The Accuracy Estimation  will open the Control Points Report. This dialog is a dynamic control that can be opened alongside the map and used to compare a set of control points or check points with a LIDAR surface. The comparisons or errors are displayed in the table and then reported as RMSE_z and Accuracy_z statistics for determining if the surface meets a given level of mapping standards. The Accuracy_z report can then be exported to a text file.

Apply Correction

Apply correction is a shortcut for a debias task. In this case by default, it will include the Mean Error measured in the Control Points Report for each axis.

Figure 7: Apply Correction dialog

How to create a control point report?

See creating a control point report.

Control Point Navigation

The Navigation tools are used to pan the map to the control point or check point record in the selected point feature class.

There are 4 navigation tools:

• First Point command: Use this command to pan the map to the first control point or check point record in the selected point feature class.
• Previous Point  command: Use this command to pan the map to the previous control point or check point record in the selected point feature class.
• Next Point command: Use this command to pan the map to the next control point or check point record in the selected point feature class.
• Last Point command: Use this command to pan the map to the last control point or check point record in the selected point feature class.

Figure 6: Navigation tools

Results

View Reports

View reports will show the available Control Points Reports available in a project.

Figure 8: View Reports

Tip

Select None to ignore any previous measurement.

How to use the Control Points Tab?

See the LP360 Short Tutorial - Control Report for a video tutorial with the Control Points Report dialog.