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

This page describes the Orbit desktop extension "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 [[261:desktop_ext:generic|]] to define the source file. 

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

===== Supplement, Group By =====

Select how the clearance obstructions are grouped 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 ** - Fixed vertical offset from the trajectory. \\
A trajectory needs to be defined in block **Trajectory**: a new path can be drawn or selected. \\
Vertical offset needs to be defined in parameters.

** Fixed height ** - Fixed z-value defined in parameters.

** Use paths ** - The source path(s) are used to set the ground reference. 

===== Parameters =====

Generic concepts, see [[261:desktop:preferences:detectors|]]

Some parameters are greyed out based on the options previously selected.

These two options are available for detection by area: range of interest is Areas/Multiple Areas and Group By is Ranges.

====Temporal Analysis====
Point cloud timestamps are analysed to make sure only points collected in the same run are used to calculate clearance. When a gap of 10 seconds is found, a new time interval is created. 

Option to save points from each time interval in a point cloud selection is available in output parameters.

====Validate Ground====
Two ground validations are done: ground Z value and ground thickness.

**- Ground expected value:** Calculated ground value per pixel will be compared to expected ground. Expected ground value is Z value from the area (the center of spatial bounds of the area), and a tolerance is used around this value to accept calculated values.

**- Ground Thickness:** From ground to minimum clearance nothing is expected, so from the minimum Z value of the pixel to the minimum clearance value above that value, the thickness of the points should not exceed Thickness Max.

Each area of interest will have a calculated percentage of valid ground, attribute: Area Pixels Ground Perc. 

When temporal analysis is also enabled, this ground validation is done per time interval, allowing us to have a better coverage of the ground of the area. And the percentage of valid ground includes calculations from all time intervals.


===== 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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