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Harris Geospatial / Docs Center / Using ENVI / ENVI LiDAR / Production Parameters Tab

Production Parameters Tab

Production Parameters Tab

In the Production Parameters tab, set the parameters to use when processing products. The parameters you need to set depend on the product formats you select in the Outputs Tab.

Processing parameters are available for the following:

Orthophoto Settings


The following settings apply when Orthophoto is a selected output.

Parameter

Description

Resolution

Select the resolution of the orthophoto that will be created, in meters. The orthophoto is based on LiDAR intensity or RGB (if supported by the point data format; otherwise, it is grayscale intensity). The highest resolution setting per pixel is 25 centimeters; the lowest is 8 meters. The default is 1 meter per pixel.

Intensity Range Min

All points with a value lower than the Intensity Range Min appear black. This setting also affects the intensity display in the Main window. Use the default value unless you see that the file is all or mostly white, in which case increase the value. You can invert the min and max intensity range values so that darker features will appear lighter. The default is 0.

Intensity Range Max

All points with a value higher than the Intensity Range Max appear white. This setting also affects the intensity display in the Main window. Use the default value unless you see that the file is all or mostly black, in which case decrease the value. You can invert the max and min intensity range values so that lighter features will appear darker. The default is 255.

DEM Settings


The following settings apply when DEM is a selected output.

Parameter

Description

Grid Resolution

Select the grid resolution to use when the DEM grid is created, in meters. The grid resolution range is 0.5 to 10 meters per pixel. Internally, a 0.5 or 1.0 meter grid resolution is used and sub-sampled to 2-10 meters, if selected. The 0.5 meter grid tunes the DEM extraction algorithms to be more sensitive at some points, and requires higher density data. If the project density is lower than 4 points / m2, selecting the 0.5 meter grid will not result in better resolution of the DEM, and the amount of time to create the DEM will increase. To save processing time, 1 meter resolution is recommended unless a very detailed 0.5 meter posting DEM is needed. The default is 1 meter.

Filter Lower Points

Select the landscape type to filter. This parameter is useful for filtering points that are lower than the terrain. Choose one of the following:

  • Do Not Filter: Disables filtering of points that are lower than the terrain. Use for low density LiDAR data (less than 5 points per square meter).
  • Urban Area Filtering: To filter, the area is divided to the grid resolution. For each cell in the grid, the points are put into a histogram and examined. Points are sorted by height, and the median point and standard deviation are found. Points that are below a multiplier of the standard deviation from the median are filtered out. If the standard deviation is too large, gaps are also counted in the histogram for better filtering. Urban areas have more false points that needed to be filtered; if you specify rural filtering in an urban area, some of the false points will not be detected.
  • Rural Area Filtering: (default) Processing is done as it is in Urban Area Filtering, the difference being how the standard deviation criterion is applied. If you specify urban filtering in a rural area, the filtering may be too aggressive, and some good terrain points in forest areas may be filtered out resulting in bumps under trees.

Near Terrain Classification

Select value for near-terrain classification, in centimeters. This is used for near-terrain classification after the DEM grid is created. Classifying points as near-terrain is useful to catch low objects that are not part of the terrain and are also not buildings, trees or power lines. For example, low vegetation, cars, buses, and so forth could all be classified as near-terrain objects When set at 50, a point is classified as terrain if it is within 50 centimeters of the grid. You can set near-terrain classification between 5 and 50 centimeters. For example, if the value is 20, points with a distance of 0 to 20 centimeters from the grid are classified as terrain points, and points with a distance of 20 to 50 centimeters are classified as near-terrain points. The default is 50 centimeters.

Contour Line Spacing

Set the vertical spacing between DEM height contour lines, in centimeters. This step is done after the DEM grid is generated; therefore, it does not affect the DEM grid generation. The default is 200 centimeters.

DEM Advanced Parameters

Click DEM Advanced Parameters to set additional parameters in the DEM Advanced Production Parameters dialog. The settings are:

  • Enable Filter Database Edges to ignore classifying points that are up to 16 meters from the edges of the dataset. In some terrain, such as forested areas with trees at the edge of the dataset, the algorithms of the DEM grid generation do not detect the edges of the database well. The check box is disabled by default.
  • Enable Variable Sensitivity Algorithm to use the variable sensitivity algorithms in the derivation of the DEM. If enabled, you need to select the DEM Sensitivity according to the mapped area. The check box is disabled by default.
  • If the Variable Sensitivity Algorithm check box was enabled, select a DEM Sensitivity value from the drop-down list. Use this parameter for low-density data (fewer than 4 points per square meter) in rough terrain with no buildings. The higher the sensitivity, the better it works with higher-frequency terrain, but increases the likelihood of falsely identifying terrain as buildings. The default is 30 - Medium.
  • Enter the Constant Height Offset, in centimeters, to specify an offset for the DEM grid in a noisy dataset. The elevation of the DEM may be slightly offset in noisy datasets due to inaccurate points above and below the ground. If this occurs, you can shift the terrain grid up or down by up to 10 centimeters. A positive number moves the DEM up, and a negative number moves the DEM down. The default is 2 centimeters.

Terrain TIN Precision

Enter a value to set the maximum allowed vertical distance between a triangle and the actual terrain. This distance between the TIN and the actual terrain introduces errors into the TIN mesh. Reducing this value will result in a more accurate TIN, but will result in an increased triangle count.

A combination of this parameter and the Maximum TIN Polygon Density will affect the TIN representation of the ground. TIN production does not affect DEM grid production. The TIN production uses only the points classified as terrain. Reducing the value of the Near Terrain Classification parameter results in reducing the number of points that are classified as terrain, thereby reducing both the time for TIN generation and the size of the TIN generated. The default is 10 centimeters.

Maximum TIN Polygon Density

Enter a value to set the maximum number of triangles that will be produced in a 100x100 meter area when producing the TIN. A combination of this parameter and the Terrain TIN Precision will affect the TIN representation of the ground. If this value is set too low, it may not be possible to achieve the Terrain TIN Precision. The default is 10000.

DSM Settings


The following settings apply when DSM is a selected output.

Parameter

Description

Grid Resolution

Select the DSM grid resolution from the drop-down list. Resolution settings range from 5 centimeters to 10 meters spacing. The default is 1 meter. This parameter can also be set from the Add Observer Points dialog for Viewshed Analysis.

When you generate a high-resolution DSM (that is, use a setting lower than 25 cm), you may need to increase the Maximum Point Density setting to get the best results from your data. Note that setting the resolution to lower than 25 cm will increase processing time.

Use Power- Lines Points

Enable the check box the to include power lines and cables as part of the DSM. If disabled, power lines and cables will not be part of the DSM (important when calculating Viewshed Analysis). The check box is enabled by default.

Trees Settings


The following settings apply when Trees is a selected output.

Parameter

Description

Height Min

Enter the expected minimum height of trees in the area, in centimeters. Points with dispersal characteristic of trees will be classified as trees. The default is 130 centimeters.

Height Max

Enter the expected maximum height of trees in the area, in centimeters. Higher points will not be classified as trees. This avoids items such as cranes being classified as trees. The default is 5000 centimeters.

Radius Min

Enter the expected minimum radius of trees in the area, in centimeters. This avoids items such as lampposts being classified as trees. The default is 200 centimeters.

Radius Max

Enter the expected maximum radius of trees in the area, in centimeters. The default is 600 centimeters.

General Settings


The following are general settings that apply to the project.

Parameter

Description

CPU Cores

(Advanced users) For PCs with multiple CPUs, set the number of CPU cores ENVI LiDAR will use for processing products.

  • To automatically use all available cores, enable the Auto CPU Cores check box. The number of cores available for the PC displays in parenthesis. For example, on a computer with 8 cores: Auto CPU Cores (8).
  • You can also enter a value in the CPU Cores field. If you enter less than the maximum cores, the remainder will be available for other processes. If you enter greater than the maximum cores, the setting defaults to the maximum available for the PC.

Clip Minimum Height

Enter a minimum height at which to filter false low points. Set the value to the lowest known point in the area. All points below this height are ignored. The default is the actual lowest point in the file.

Clip Maximum Height

Enter a maximum height at which to filter high-altitude noise. Set the value to the highest known point in the area. All points above this height are ignored. The default is the actual highest point in the file.

Maximum Point Density

Use this parameter to limit the number of processed and viewed points. For example, it is useful if you want to reduce processing time for buildings and power lines when the point density is high (such as, 50 points per meter or greater). The limit is applied by taking only some of the points per block of per block of data (a single block is 32x32 meters). Limiting the density shortens the processing time of the buildings and power line detection algorithms, but might also limit the number of extracted features. Used mostly with terrestrial and mobile scanning databases, as the density is much higher closer to the scanner..

Specify a value in points per square meter or Ground Sample Distance (GSD), in meters. The points used in the product extraction calculations will be thinned according to the value entered and those points that have been excluded from the calculations will be classified as unprocessed. Select one of the following from the drop-down list, then enter the value in the field provided.

  • Points/m2: Specifies the maximum number of points per square meter. The larger the value, the more points that will be included in processing. The default is 50 points per square meter, regardless of the density of the input.
  • Ground Sample Distance (m): Specifies a GSD, in meters. The smaller the value, the more points that will be included in processing. The default is 0.141421 meters.

Buildings Settings


The following settings apply when Buildings is a selected output.

Parameter

Description

Minimum Area

Set the minimum area for building planes (the flat, two-dimensional surfaces), in meters. The buildings algorithm searches for all flat surfaces, then measures the area of each flat surface. Surfaces with an area less than this value are filtered out before processing continues. The default is 10 meters.

Near Ground Filter Width

Set the near-ground filter width, in centimeters. This is useful for preventing buses, trucks, train cars, and so forth from being classified as buildings. Near-ground filtering occurs after Minimum Area filtering. Objects less than 5 meters above the ground that have a width less than this value are filtered out of the building classification. The default is 300 centimeters.

Buildings Points Range

This setting is useful for detecting building planes when the point density is not equal throughout the data. Typically, this value should be Auto; however, if the data density is low (1 point per m2 or lower), large buildings such as hangars or warehouses may not be classified as buildings. Increasing this value to 1.2 or 1.4 will help detect them, but also increases the likelihood of falsely identifying trees as buildings. The range is 0.5 to 1.4; the default is Auto.

Plane Surface Tolerance

Set the plane surface tolerance, in centimeters. This is the allowed vertical tolerance for searching for the surface in the neighboring points. This setting is useful for databases that have higher noise, and also when the nature of surfaces requires a higher tolerance, such as curved surfaces. If trees are present, increasing this value also increases the likelihood of falsely identifying trees as buildings. The range is 15.0 to 60.0; the default is 30 centimeters.

Buildings as Box Models

Enable the check box to calculate buildings as a perimeter line with one flat roof shape. This setting is useful when you do not want to divide buildings into sub surfaces and leave them as flat roof bounding contours. The classification is the same, but only one contour is generated at the requested height with one of the following options:

  • Height at Average Roof: Set the contour at the average height of the roof.
  • Height at Top Roof: Set the contour at the highest point of the roof.
  • Height at Bottom Roof (default): Set the contour at the lowest point of the roof.

Power Lines Settings


The following settings apply when Power Lines is a selected output.

Parameter

Description

Search Wide Power Lines

Enable the check box to search power lines in noisy data where points that belong to one power line may be horizontally scattered over one meter. You will get one vector for triple conductors attached together in transmission lines. Use this parameter with caution as it may connect several lines together. This parameter is not optimized for low KV power lines. Do not use this parameter and Search Low KV Power Lines together. The check box is disabled by default.

Process Power Poles

Enable the check box to process power poles by searching for them, or by using the imported power poles locations reference list. Output is saved to CVS and SHP. If this check box is disabled, no power pole output is created. The check box is disabled by default.

Search Low KV Power Lines

Enable the check box to search for low voltage power lines that are close to each other. This will be able to separate the lines only if the point density is high and the noise it low. Otherwise, expect that power lines may cross each other. Do not use this parameter and Search Wide Power Lines together. The check box is disabled by default.

Search Additional Power Poles

Enable the check box to look for power poles in addition to the imported power poles locations list. This option is disabled if you did not import a power poles locations list. The check box is disabled by default.

Poles Classification Base Radius

If the Process Power Poles check box is enabled, enter the Poles Classification Base Radius, in meters. This parameter is used for classification after the power pole was identified. The classification is done in a cylinder around the pole center. This parameter controls the lower part of the pole from the ground level to the half of the pole height. If the radius of the power pole is known, set the parameter to the known radius of the base. For large pylons, if this parameter is not increased high enough not all of the points on the pylon will be classified as power pole. The default is 3 meters.

Poles Max Radius Top

If the Process Power Poles check box is enabled, enter the Poles Max Radius Top value, in meters, that defines the maximum radius of pole's arms. In most situations, there is no need to change it, as it is selected automatically by the attachment point spreading. Set this parameter so the algorithm will not join attachment points with the wrong placement of the power pole base. This will happen if there are two parallel lines with separated power poles. The default is 10 meters.

Extend Poles Classification Beyond Attachment Points

If the Process Power Poles check box is enabled, enter the Extend Poles Classification Beyond Attachment Points, in meters. At the higher part of the power pole, points located this distance from the attachment points will be classified as power line points. The default is 0 meters.

Extend Wires to Poles Distance

If the Process Power Poles check box is enabled, enter the value, in meters, to Extend Wires to Poles Distance. This value sets the maximum power line gap to be corrected. Capability is provided to bridge gaps in the line from the end of the detected line to the next power pole. This assumes the power lines are not continuous for reasons such as:

  • Points may not be recorded if the LiDAR sensor was too close to the high points on the power line.
  • The LiDAR sensor's view of one power line may be obscured by another line.

The default is 40 meters.

Power Lines Minimum Height

Enter the minimum height for power lines, in meters. This is the minimum height at which to detect power lines. The default is 6 meters.

Power Lines Advanced Parameters

Click Power Lines Advanced Parameters to set additional parameters in the Power Lines Advanced Production Parameters dialog. The settings are:

  • Enable the Filter Trees Below Power Lines check box to filter trees below power lines. This prevents trees considerably lower than power lines from becoming extended up to them. The filter attempts to vertically separate tree and power line points, but sometimes incorrectly removes the entire tree even when it is adjacent to power lines, rather than directly below them. If the results of tree extraction are noticeably worse when extracting trees and power lines compared to extracting only trees (such as large gaps of unclassified points), then disable this check box.
  • Enter the Power Lines Min Length, in meters, to specify the minimum length a power line segment must be to be classified. Detected power line segments shorter than this value will not be classified as power lines. The default value is 10 meters, and the minimum value is 1 meter.

    Note: Setting this value very low may result in the detection of many false positives.

  • Enable the Filter Power Lines By Min Joined Length check box to filter power lines by minimum joined length. Power lines are generated by extracting individual power line segments, then joining appropriate segments together. The minimum joined length refers to the entire length of the power line composed of multiple power line segments.

  • Enter the Power Lines Min Joined Length, in meters, to specify the minimum length a span of joined power line segments must be to be classified. Joined power lines segments shorter than this value will not be classified as power lines. The default value is 20 meters, and the minimum value is 1 meter.

    Note: Setting this value very high may result in filtering out many genuine power lines.



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