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

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

{{orbitgis:how_to_find.png?25&nolink|}} [[2210:desktop:workspace:main_toolbar|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 [[2210: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 of points ===

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

=== Areas of interest ===

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).

=== 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.

=== Margin ground ===

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

The advanced set of parameters can be accessed by small grey circle above basic parameters.\\

Algorithm:
  * **Pixel Pts Min**: The minimum number of points from the point cloud within the column above a pixel, pixels that include less points are not used to define floor and ceiling.
  * **Slice Thickness**: The thickness of horizontal slices to define ground and ceiling within each pixel.
  * **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.

  * **Fixed Ground Height**: Value used as the Ground Reference (default = -999).
  * **Trajectory Offset**: Vertical offset from the trajectory height.

Output:\\
  * **Missing Sample**: The value that will be used for the clearance.omi raster created if there are no overhanging objects (default = -999).

===== 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.
  * **OK**: Flag on for checked points.
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.
Merging projects can be done by clicking the yellow merge icon.

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