Description Usage Arguments Details Value References Examples
FilterData applies various filters to return data files to produce new return data files with only the returns that meet the filter requirements. The most common application for FilterType is to remove “outliers” from return data files. Other filter options overlay the return data with a user-specified grid and produce output return files that contain only the returns with the minimum or maximum elevation for each grid cell.
1 2 3 4 5 6 7 8 9 | filterData(
fusion.path = "C:/FUSION/",
FilterType,
FilterParms,
WindowSize,
OutputFile,
DataFile,
switches = NULL
)
|
fusion.path |
Character. The directory where FUSION is installed. By defult: C:/FUSION/ |
FilterType |
Character. Filtering algorithm used to remove returns from the DataFile(s).
|
FilterParms |
Numeric. Parameters specific to the filtering method. For outlier this is the multiplier applied to the standard deviation. For minimum and maximum, FilterParms is ignored (but a value must be included on the command line...use 0) |
WindowSize |
Numeric. Size of the window used to compute the standard deviation of elevations or the minimum/maximum return |
OutputFile |
Character. Name of the output file. If any part of the name includes spaces, include the entire name in double quotation marks. Must have the extension. |
DataFile |
Character. LIDAR data file name or template or name of a text file containing a list of file names (list file must have .txt extension). |
switches |
Character. Default is NULL. To insert a switch, each switch must have a '/' before of the names. If you want to insert two or more switches, they must be separated by an empty space. When a # is displayed, should be replaced by the desired value depending on see switch.
|
FilterData was developed to help LIDAR data users eliminate outliers from files delivered by vendors. In general, vendors identify outliers (returns above expected elevations for vegetation and structures or returns below the ground surface)
and either use the LAS classification field to label the return as an outlier or delete them from the files delivered to their client.
However, sometimes not all outliers are removed. The presence of unlabeled outliers can cause problems for bare-earth filtering algorithms and vegetation analysis as well as other analyses. FilterData offers a way for the data user to produce “clean” data files for use in subsequent analyses.
FilterData provides an outlier filter that identifies and removes returns based on the range of observed elevation values in the comparison window. In operation, the outlier filter works by computing the mean elevation and standard deviation of elevations for each cell in the comparison grid.
Then, individual return elevations are compared to range defined as follows:
mean elevation ± (FilterParms * ElevationStandardDeviation)
Only returns with elevations within the range are written to the output file. Generally, using a range of ± 5.0 * Standard deviation and a large window size (100 m) eliminates most outliers. In areas if steep terrain with returns from birds, a range of ± 3 * Standard deviation may produce better results.
The outlier filter can also be used on return files produced using the maximum filter to eliminate high returns from small objects such as transmission towers and lines. Flat areas with no above-ground features can result in a very low standard deviation of the return elevations.
For data files containing such areas, it may be necessary to use the /minsd:# switch to control filtering in cells with small standard deviations. The default is to use a minimum threshold standard deviation of 1.0 (same units as the return elevations). For most areas, this will be sufficient. If you specify a smaller threshold, you may find that all returns within the comparison window are removed.
FilterData also provides a minimum and maximum classification feature that produces output files that contain only the return with the minimum or maximum elevations for each cell in the comparison grid.
No return value. This function return the command prompt running the FUSION command
McGaughey, R.J. FUSION/LDV: Software for LIDAR Data Analysis and Visualization. 2021.
1 2 | filterData(FilterType = 'outlier2',FilterParms = 3,WindowSize = 5,
OutputFile = 'Z:/filterdata.las',DataFile = 'Z:/datafile.las', switches = '/invert /layers')
|
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