v.outlier(1grass)

💅 v.outlier 💅

okay bestie, so this is v.outlier, a GRASS User's Manual page, and it's literally the girl who removes outliers from vector point data. no cap. ✨

🎀 KEYWORDS 🎀

vector, statistics, extract, select, filter, LIDAR

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✨ SYNOPSIS ✨

v.outlier
v.outlier --help
v.outlier [-e] input=name output=name outlier=name  [qgis=name]
[ew_step=float]   [ns_step=float]   [lambda=float]   [threshold=float]
[filter=string]   [--overwrite]  [--help]  [--verbose]  [--quiet]
[--ui]

🚩 Flags

• -e — Estimate point density and distance. It estimates the point density and distance for the input vector points inside the current region extends, and then it dips. bye! ✌️
• --overwrite — lets output files overwrite files that already exist (yes, it's giving bold)
• --help — prints the usage summary, for when you're like "wait what"
• --verbose — verbose module output, aka the module tells you everything
• --quiet — quiet module output, aka the module tells you nothing 🫶
• --ui — forces launching the GUI dialog

🧚 Parameters

• input=name [required] — Name of input vector map. Or a data source for direct OGR access, iykyk.
• output=name [required] — Name for output vector map.
• outlier=name [required] — Name for output outlier vector map. that's where the rejected points go 😭
• qgis=name — Name for vector map for visualization in QGIS 👑
• ew_step=float — Length of each spline step in the east-west direction. Default: 10 * east-west resolution.
• ns_step=float — Length of each spline step in the north-south direction. Default: 10 * north-south resolution.
• lambda=float — Tykhonov regularization weight. Default: 0.1.
• threshold=float — Threshold for the outliers. Default: 50.
• filter=string — Filtering option. Options: both, positive, negative. Default: both.

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🌸 DESCRIPTION 🌸

so basically, v.outlier removes outliers in a 3D point cloud. 💖

by default, the outlier identification is done by a bicubic spline interpolation of the observation with a high regularization parameter and a low resolution in south-north and east-west directions. and then — the way that — any point that differs in an absolute value more than the given threshold from a fixed value (reckoned from its surroundings by the interpolation) is considered an outlier and gets removed. periodt. 💅

the filter option says whether all outliers get removed (that's the default), or only positive ones, or only negative ones. filtering only positive outliers can be useful to filter out vegetation returns (like, from forest canopies 🌳) out of LIDAR point clouds, so you can extract digital terrain models (DTMs). filtering only negative outliers can be useful to estimate vegetation height. obsessed with the use cases honestly.

there's also a flag to create a vector that can be visualized in QGIS. what that means is topology gets built and the z coordinate is considered as a category. main character energy tbh. ✨

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💖 EXAMPLES 💖

Basic outlier removal

v.outlier input=vector_map output=vector_output outlier=vector_outlier thres_O=25

in this case, a basic outlier removal is done with a threshold of 25 m. cute, simple, slay.

Basic outlier removal

v.outlier input=vector_map output=vector_output outlier=vector_outlier qgis=vector_qgis

now the outlier removal uses the default threshold, and there's also an output vector available for visualization in QGIS (http://www.qgis.org). 🦋

North Carolina dataset example

v.outlier input=elev_lid792_bepts output=elev_lid792_bepts_nooutliers \
  outlier=elev_lid792_bepts_outliers ew_step=5 ns_step=5 thres_o=0.1

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📝 NOTES 📝

this module is designed to work with LIDAR data, so no topology is built — except in the QGIS output. that's the one exception, bestie. 💀

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👀 SEE ALSO 👀

v.surf.bspline

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👑 AUTHORS 👑

Original version of the program in GRASS 5.4:

Maria Antonia Brovelli, Massimiliano Cannata, Ulisse Longoni and Mirko Reguzzoni

Updates for GRASS 6:

Roberto Antolin

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🔥 SOURCE CODE 🔥

Available at: v.outlier source code (history)

Latest change: Friday May 09 14:33:40 2025 in commit:

b356c7e108fcbeca77474c8e83ebec8f1e7b3e4a

Main index | Vector index | Topics index | Keywords index | Graphical index | Full index

© 2003-2026 GRASS Development Team, GRASS 8.5.0 Reference Manual

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okay that's the whole thing, no notes, go remove some outliers bestie 🫶✨ this was v.outlier from the GRASS 8.5.0 Reference Manual, last touched Friday May 09 14:33:40 2025 in commit b356c7e108fcbeca77474c8e83ebec8f1e7b3e4a, © 2003-2026 GRASS Development Team. mwah 💋