====== Clearance Checker ====== 

This page describes the Orbit desktop extension "Clearance Checker". 

{{orbitgis:how_to_find.png?25&nolink|}} Main Toolbar > Extensions > Clearance Checker

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===== Concepts =====

The Clearance checker extension calculates the lowest clearance of overhanging objects or constructions above a surface.\\

===== Source =====

Use the generic workflow for [[234:desktop_ext:generic|]] to define the source file. 

The method for the range of interest is 'Path', 'Multiple Paths', 'Area' and 'Multiple Areas'. 

===== Group By =====

=== Clusters ===

For every area or path, the point cloud gets divided into clusters. For each cluster, the lowest clearance will be calculated. \\

=== Ranges ===

For every area or path, the lowest clearance will be calculated.

===== Ground Reference =====

Choose one of the below-described options to define the Ground Reference:
=== Point Cloud lowest Z ===

The lowest z-value of the point cloud.

=== Point Cloud Z below trajectory ===

The lowest z-value of the first point cloud cluster found below the trajectory.

=== Trajectory offset ===

Enter a fixed vertical offset from the trajectory - Ref. Advanced Parameters (see below).

A trajectory needs to be defined in block **Trajectory**: a new path can be drawn or selected.

=== Fixed height ===

Enter a fixed z-value - Ref. Advanced Parameters (see below).

=== Use paths ===

The source path(s) are used to set the ground reference. 

===== Parameters =====

Define parameters for the detection:

=== Pixel Size ===

The pixel size defines the grid size of the DEMs that are created. For every pixel, the lowest clearance is calculated.

=== Ground margin ===

The vertical offset between the Ground Reference that will be excluded from the analysis. 

=== Slice Thickness ===

Horizontal sliced are used to define ground and ceiling within each pixel. If a slice with a minimum number of points is found above ground height, then the clearance for that pixel is defined.

=== Fixed Ground Height ===
The value for the fixed ground height, available when ground reference is Fixed height.

=== Trajectory Offset ===
The fixed offset from trajectory, available when ground reference is Trajectory offset.

===== Advanced Parameters =====

The advanced set of parameters can be accessed by small grey circle in top right corner of block Parameters.\\

=== Algorithm ===
  * **Pixel Pts Min**: The minimum number of points from the point cloud within a pixel. Pixels that include less points are not used to define floor and ceiling.
  * **Slice Pts Min**: The minimum number of points in a horizontal slice to define floor and ceiling of a pixel.
  * **Clearance Pixels Min**: The minimum number of pixels a cluster should have. The final floor and ceiling are defined by a cluster of pixels.
  * **Point distance**: The distance between line points to check clearance by line.
  * **Context radius**: The radius to use around line points to check clearance.
  * **Context Pts Min**: The minimum number of points in the context of a line point.
  * **Clearance Max**: If not zero, clearances above this value will not be considered.

=== Output ===
  * **Missing Sample**: The value that will be used for the clearance.omi raster created if there are no overhanging objects (default = -9999).
  * **Get point cloud as selection**: Get a point cloud selection file of the clearance points.
  * **Get point cloud attributes**: Get a point cloud attribute file with clearances.
  * **Get intermediate rasters**: Get rasters created to detect clearance. Only available for clearances by area and clusters.

===== Results =====

The Hit count is the number of clearances found. 

  * **Z range**: Value of the clearance.
  * **#pnts**: Number of points defining the ceiling of the clearance.

DEM files are added to the Dataset List by default and are saved in the corresponding folder (see above). 
  * **Clearance**
  * **Cluster_min_clearance**
  * **Ground**
  * **Pixel_z_range**

===== Clearance Checker Tab =====

In the Clearance Checker Tab all Clearance Projects are shown including the results and metadata. Standard operations like detaching and maximizing tab are available.

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