HAS-QGIS-scripts

Raster Barplot for QGIS

A QGIS Processing script that mimics GRASS’s r.barplot. It draws a barplot or piechart of a statistic computed for each category of a zonal (categorical) raster, and renders it in an interactive matplotlib window inside QGIS.

Features

• One bar or pie wedge per category of a zonal raster.
• Statistic per zone: cell count, or the sum, mean, minimum or maximum of an optional value raster.
• For count, choose a reporting unit: cells, percent of total, or area in m², ha or km² (derived from the zones raster’s pixel size).
• Bar or pie plot type; horizontal bars; grid lines; value labels on the bars/wedges.
• Sort bars/wedges by value (ascending or descending), or keep natural order.
• Fill from a single color, the zonal raster’s color table (-c equivalent), or the active matplotlib style palette; separate border color and width.
• Title, axis labels, font size, title font size, font family, and matplotlib style sheet (e.g. ggplot).
• Interactive matplotlib window with pan, zoom, and save toolbar, or export to PNG / PDF / SVG.

Requirements

• QGIS 3.x with the Processing framework (bundled).
• Python packages: numpy, matplotlib, gdal, PyQt5 — all shipped with standard QGIS installations.

Installation

1. Download raster_barplot.py from github
2. In QGIS, open the Processing Toolbox (Ctrl+Alt+T).
3. Click the Python icon at the top of the toolbox and choose Add Script to Toolbox….
4. Select raster_barplot.py.

The algorithm appears under Scripts → Raster plots → Raster barplot.

To update the script later, edit it in place (right-click → Edit script) or re-add it via the same menu.

Usage

Open the algorithm and set:

• Zonal raster — the categorical raster; one bar/wedge per category.
• Value raster (optional) — required for the sum, mean, minimum and maximum statistics.
• Statistic — count, sum, mean, minimum, maximum.
• Unit — for count only: cells, percent, m2, ha, km2.
• Plot type — bar or pie.
• Sort order — natural, ascending, descending.
• Flags for horizontal bars, grid, value labels, and label rotation.
• Bar/wedge color — a single fill color, or enable Color bars/wedges from zonal raster color table to use the zones layer’s current QGIS style (paletted or singleband pseudocolor) or its embedded GDAL color table.
• Border color / Border width — outline of the bars/wedges.
• Title, axis labels, font size, title font size, font family, and a matplotlib style sheet.
• Output image (optional) — leave empty for an interactive window, or provide a path to save as PNG, PDF, or SVG.

Notes

• The value raster must share shape (rows × columns) with the zones raster. If not, align them first with Processing → Align rasters.
• Area units (m²/ha/km²) come from the zones raster’s pixel size in its CRS units. For a raster in a geographic CRS (degrees) those areas are not meaningful; a warning is logged. Reproject to a projected CRS first.
• The Unit option applies only to statistic=count; it is ignored for the other statistics.
• A piechart requires non-negative values, and axis labels do not apply to it.
• When zonal colors are enabled but a zone has no color in the layer’s style or color table, that bar/wedge falls back to gray with a warning in the log.

AUTHOR

Paulo van Breugel, HAS green academy, Innovative Biomonitoring research group, Climate-robust Landscapes research group

This site is open source. Improve this page.