Introduction to
GRASS GIS

Helena Mitasova
and Vaclav Petras

GIS/MEA582 Geospatial Modeling and Analysis NCSU

Learning Objectives

This lecture is a brief introduction to GRASS GIS software and overview of its features in the context of this course and open source software in general.

Open Source and Licensing

• According to Stallman (2002), there are four freedoms that as a user you should have:
  • the freedom to use the software for any purpose,
  • the freedom to change the software to suit your needs,
  • the freedom to share the software, and
  • the freedom to share the changes you make.

Stallman, R. M. (2002). Free software, free society: selected essays. Ed. by J. Gay. 1st. ed. OCLC: 253840339. Boston, Mass: Free Software Foundation. 220 pp. ISBN 978-1-882114-98-6.

Commercial and FOSS

• FOSS can be used commercially
• FOSS can be commercial but not proprietary
• FOSS can be used to build closed platforms
• Widely used FOSS examples:
  • Red Hat Enterprise Linux/CentOS
  • Android/Android Open Source Project
  • Chrome/Chromium, Firefox
  • WordPress, Drupal
  • Moodle
  • Python, R
  • Apple, Google, Facebook, Amazon, Netflix

GRASS GIS

GRASS GIS (Geographic Resources Analysis Support System) is a Free and Open Source Software suite for geospatial data management and analysis, image processing, spatial modeling, and visualization.

grass.osgeo.org

Source code in github

GRASS GIS

• 1983 started at US Army CERL as land management system
• evolved into general purpose GIS
• 1999 GNU GPL, international team of developers
• 2008 OSGeo Project
• 40+ years of GRASS GIS development

Historical Video

Historical promotional video from 1987 narrated by William Shatner

watching 1 minute is sufficient to get the idea, optionally you can watch the whole 15 minutes and see metadata and transcript at doi.org/10.5446/12963

Software Implementation

• portable:
  • many operating systems: MS Windows, Mac OS, Linux, ...
  • high-end desktops, low-end laptops, Raspberry Pi, High-Performance Computing clusters, ...
• single integrated software
• functionality implemented as 500+ tools (modules)
• written in C and Python

Processing Capabilities

raster and 3D raster

map algebra, DEM, interpolation, flow, neighborhood, solar, cost surfaces, ...

imagery (remote sensing)

rectification, multispectral, classification, segmentation, PCA, FFT, ML, ...

vector and database

buffers, overlays, networks, topology, attribute management, SQL, ...

spatio-temporal data (time series)

sampling, statistics, aggregation, temporal topology, algebra, ...

General Capabilities

visualization

2D display, 3D visualization, temporal visualization, PNG, PS and PDF maps, ...

interoperability

import from and export to different formats, WMS, ...

extensibility

scriptable (e.g. Python), custom tools (typically Python or C), ...

Naming Convention for Tools (Modules)

User Interfaces

Tools (modules) can be accessed using:

• Graphical User Interface (GUI)
• Command Line Interface (CLI)
• Python
• Third party interfaces (QGIS, R, ...)

Graphical User Interface

• The interface for a desktop

GUI for tools (modules)

• All tools have standardized, unified interface layout.

Standard dialog (form) for the r.neighbors tool (module) generates also the command line version

Command Line

• The baseline interface for efficiency and reproducibility
• Available in GUI as Console with autocomplete functions

  r.fill.dir input=elev output=fill direction=dir
  

• and in terminal in Linux or Mac

Python

• grass package part of GRASS GIS
• access to tools (modules), but also to internal C functions
• integrated Python editor
• integrates with Jupyter Notebooks

import grass.script as gs
gs.run_command('r.fill.dir', input='elev',
               output='fill', direction='dir')

Duality between GUI and commands

Command line (Bash):
Python:

Examples in documentation and class instructions are provided as commands which can be used to fill-in GUI, write Python code, or run directly.

3rd Party Interfaces

• QGIS (Processing Plugin and GRASS Plugin)
• R (rgrass package)
• ...

3rd Party Interfaces

• Tangible Landscape
  • tangible user interface to GRASS GIS and Blender
  • by NC State University, Center for Geospatial Analytics

Tools running: v.surf.rst, r.contour, r.fill.dir, r.sim.water
see also Petrasova et al., 2018, Tangible Modeling with Open Source GIS, 2nd edition, Springer

Documentation: Users manual

Public Author & Accessible Code

Link to Research Papers

Continuing development

• Used as a research platform and code repository
• Example: Solar radiation model r.sun
  • available since 1993
  • major changes in 1996, 1999, 2002, 2003, 2006, 2008, 2017
  • parallelized version in 7.4
  • Hofierka, J., Suri, M. (2002): The solar radiation model for Open source GIS: implementation and applications. International GRASS users conference in Trento, Italy, September 2002.

Example application: summer solstice solar radiation dynamics on lidar DEM (Centennial Campus)

Addons Repository

• 300+ user contributed tools
• integrated with g.extension
• including compiled C and C++ for MS Windows
• automatically generated GUI for Python and C/C++

Try GRASS GIS with Jupyter Notebooks

• GRASS GIS: From Beginner to Power User (FOSS4G 2022 workshop)
• GSoC project: Improved integration of GRASS GIS and Jupyter

Summary

• General free and open source concepts
• Licensing: No "purchasing of licenses" needed for users
• Brief GRASS GIS overview: example open source geospatial software
  • processing capabilities
  • several user interfaces
    • Class instructions are using GUI and command line
    • Python and Jupyter are recommended for the projects
  • addon tools