d.polar(1grass)

📦
version 8.5.0 · 10 versions
, in alpine 3.24, ubuntu stonking

💖 d.polar — the manual, but make it cute 💖

okay bestie, welcome to d.polar, from the GRASS User's Manual (aka the GRASS 8.5.0 corner of the universe). it draws a polar diagram of an angle map — like aspect or flow directions — and honestly? it's giving data visualization main character energy 👑

✨ NAME ✨

d.polar — draws polar diagram of angle map such as aspect or flow directions. literally that's the whole job and she does it flawlessly 💅

🌸 KEYWORDS 🌸

display, diagram

🦋 SYNOPSIS 🦋

d.polar
d.polar --help
d.polar [-x] map=name  [undef=float]   [output=name]   [--overwrite]  [--help]  [--verbose]  [--quiet]  [--ui]

🎀 Flags 🎀

  • -x — Plot using Xgraph ✨
  • --overwrite — Allow output files to overwrite existing files (she will simply replace them, no cap)
  • --help — Print usage summary
  • --verbose — Verbose module output (she tells you everything 🗣️)
  • --quiet — Quiet module output (she says nothing, iconic silence 💀)
  • --ui — Force launching GUI dialog

💜 Parameters 💜

  • map=name [required] — Name of raster angle map. like, you GOTTA give her this one, it's mandatory bestie 🫶
  • undef=float — Pixel value to be interpreted as undefined (different from NULL)
  • output=name — Name for optional EPS output file

🌈 DESCRIPTION 🌈

so. d.polar calculates and displays a polar diagram of an angle raster map — think aspect, wind direction, or flow. the vibe is immaculate. BUT here's the tea ☕: the input angle map orientation must be counter-clockwise (CCW) from east, and the angle map units must be degrees. this refers to the standard orientation of GRASS (e.g., see r.slope.aspect). don't come at her with radians, she will not be okay 😭

The radius of the outer circle is defined by the total number of pixels in the map. so if the polar diagram does not reach the outer circle? no data (NULL) pixels were found in the map. that's the whole mystery solved, periodt 🔍

The vector in the diagram indicates a prevailing direction, and its length is the strength of such direction. in case all angle vectors are oriented along the same direction, the length for the vector is maximal — in fact it is equal to length of the most populated bin of the underlying histogram. she ate that fr fr 📏✨

As a side effect, the quality of the angle map can be derived from the diagram. strong spikes may indicate an over-representation of the related angle(s), which happens in particular if integer maps are used. so like, spikes = sus. keep an eye on them 👀

💅 NOTES 💅

If the output parameter is used, the diagram is generated as EPS file. If the -x flag is used, xgraph is launched. Otherwise d.polar will use d.graph to draw the plot in the current display frame. three paths, one queen 👑

If d.polar is used on an aspect map generated by r.slope.aspect, the undef parameter should be set to 0 to distinguish NO DATA (NULL) areas from areas where aspect is undefined (i.e. flat areas). this is the tip that saves lives, iykyk 🧚

Polar diagram of aspect map 🌸 (that's the figure caption bestie, she's just standing there, being pretty)

⭐ EXAMPLE ⭐

In this example, the polar diagram of the 'aspect' angle map in the North Carolina sample dataset is generated:

g.region raster=aspect -p
d.polar aspect

🔥 XGRAPH REQUIREMENT 🔥

Xgraph must be installed for the -x flag to function. no xgraph, no x-flag. that's the rules 💀

🌈 SEE ALSO 🌈

d.graph, d.histogram, d.rast.arrow, r.slope.aspect

🍓 REFERENCES 🍓

J. Hofierka, H. Mitasova, and M. Neteler (2009): Terrain parameterization in GRASS. In T. Hengl and H.I. Reuter, editors, Geomorphometry: concepts, software, applications. Elsevier (DOI)

👑 AUTHORS 👑

  • Markus Neteler, ITC-irst, Italy
  • Bruno Caprile, ITC-irst, Italy
  • Hamish Bowman, Otago University, New Zealand

the founding mothers and fathers of the polar diagram, we stan 🫶

🧚 SOURCE CODE 🧚

Available at: d.polar source code (history)

Latest change: Thursday Nov 06 22:27:54 2025 in commit: 298b38614712934179355ea767403d6bfea8f5f9

Main index | Display index | Topics index | Keywords index | Graphical index | Full index

okay that's the whole page bestie!! 💖 this was d.polar from the GRASS 8.5.0 Reference Manual, © 2003-2026 GRASS Development Team, and the manual itself is rocking GRASS 8.5.0. go draw some polar diagrams and slay ✨🎀🦋

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