v.hull(1)

📦
version 8.4.2 · 8 versions
, in fedora 44

✨ v.hull(1) ✨ — a page from the GRASS GIS User's Manual 💖

okay bestie, buckle up, we're doing convex hulls today and honestly? it's giving geometry queen 👑

💫 NAME 💫

v.hull — makes a 2D/3D convex hull for a vector map you hand it. that's it, that's the job. slay. ✨

🏷️ KEYWORDS 🏷️

vector, geometry, 3D 🦋

📜 SYNOPSIS 📜

v.hull
v.hull --help
v.hull [-rf] input=name  [layer=string]  output=name  [cats=range]
[where=sql_query]   [--overwrite]  [--help]  [--verbose]  [--quiet]
[--ui]

🚩 Flags:

  • -r — limit it to the current region 🎯
  • -f — make a 'flat' 2D hull even if your input is 3D points (no cap, it will simply flatten the situation 💅)
  • --overwrite — let output files overwrite files that already exist, so rude but so useful
  • --help — print the usage summary, your lil cheat sheet 🫶
  • --verbose — verbose module output, she's chatty
  • --quiet — quiet module output, she's mysterious 🤫
  • --ui — force launching the GUI dialog, for the visual girlies 🎀

🧩 Parameters:

  • input=name [required] — name of input vector map. or a data source for direct OGR access, iykyk.
  • layer=string — layer number or name ('-1' for all layers). a single vector map can be connected to multiple database tables, and this number decides which table to use. when you're doing direct OGR access, this is the layer name instead. default is -1. 🙈
  • output=name [required] — name for output vector map. give it a cute one 💖
  • cats=range — category values. example: 1,3,7-9,13
  • where=sql_query — WHERE conditions of an SQL statement, no 'where' keyword needed. example: income < 1000 and population >= 10000

🌈 DESCRIPTION 🌈

so v.hull computes the convex hull of a vector map and spits out that convex hull polygon as a vector area map. and what even is a convex hull, you ask? it's also called a convex envelope — and for an object or a set of objects it's the minimal convex set containing the given objects. iconic definition, honestly. this module builds a vector polygon that contains all the vector points or lines from your input map. all of them. periodt. 💅

now, when your input points are 3D, the hull is gonna be 3D too — unless you go ahead and pass the -f flag. and heads up: the 3D hull will be composed of triangular faces. 🔺

Fig: Convex hull polygon created with v.hull 🌸

📌 NOTES 📌

okay real talk, listen closely: to use the where option, you must set the layer option to a positive number. the default is '-1' for 'all layers', and if you leave it there then all the points from all the layers get used, and your cats and where options get completely ignored. not a vibe. set the layer. 🚨

🧪 EXAMPLE 🧪

here's an example of v.hull 3D output, using two random 3D point clouds from the North Carolina sample data set:

g.region rural_1m -p
r.mapcalc "zero = 0"
v.random -z output=random3d_a n=10 zmin=0 zmax=200
v.random -z output=random3d_b n=15 zmin=400 zmax=600
v.hull input=random3d_a output=random3d_a_hull
v.hull input=random3d_b output=random3d_b_hull
d.mon wx0
d.vect random3d_a_hull
d.vect random3d_a color=red
d.vect random3d_b_hull
d.vect random3d_b color=red
# 3D view in wxGUI (g.gui)

Fig: Convex hull in 3D from 3D points created with v.hull 🔥

📚 REFERENCES 📚

  • M. de Berg, M. van Kreveld, M. Overmars, O. Schwarzkopf, (2000). Computational geometry, chapter 1.1, 2-8.
  • J. O'Rourke, (1998). Computational Geometry in C (Second Edition), chapter 4.

👀 SEE ALSO 👀

v.delaunay

👑 AUTHORS 👑

  • Andrea Aime, Modena, Italy
  • Markus Neteler, ITC-irst (update to 5.7)
  • Benjamin Ducke, CAU Kiel (3D hull support)
  • Martin Landa, CTU in Prague, Czech Republic (vector lines support)

💾 SOURCE CODE 💾

available at: v.hull source code (history) 🦋

accessed: Saturday Jan 17 05:41:22 2026

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

that's the whole page bestie, go build yourself a hull and be the main character of your own point cloud 💖

© 2003-2025 GRASS Development Team, GRASS GIS 8.4.2 Reference Manual — and this whole thing lives under GRASS 8.4.2, landing on your screen as v.hull(1). mwah 💅✨🎀

📦 where this page comes from