Free Geography Tools

The last in this series (parts one, two, three, and four). The previous applications have been primarily focused on remote sensing applications, but there are also a number of general purpose freeware GIS programs that include significant remote sensing analysis capabilities.

GRASS

A powerful but often difficult to use GIS program. Quantum GIS is implementing an easier interface for GRASS’s capabilities. A Java version of GRASS (JGRASS) is being built on top of uDIG, but is concentrating on hydrogeological and geomorphological capabilities for now.

• Canonical component analysis (CCA)
• Color composite generation
• Edge detection
• Frequency filtering (Fourier, convolution matrices)
• Fourier and inverse fourier transformation
• Histogram stretching
• IHS transformation to RGB
• Image rectification (affine and polynomial transformations on raster and vector targets)
• Ortho photo rectification
• Principal component analysis (PCA)
• Radiometric corrections (Fourier)
• Resampling
• Resolution enhancement (with RGB/IHS)
• RGB to IHS transformation
• Texture oriented classification (sequential maximum a posteriori classification)
• Shape detection
• Supervised classification (training areas, maximum likelihood classification)
• Unsupervised classification (minimum distance clustering, maximum likelihood classification)

gvSIG

gvSIG is moving towards release of version 2.0, which will add a substantial number of remote sensing analysis functions. If you want to look at an early version, there’s a 1.9 alpha release available.

- Clipping of bands and data
- Export layers
- Save from view to raster file
- Color table and gradient edition
- No data values management
- Pixel process (filters)
- Color interpretation management
- Overview creation
- Enhanced radiometric
- Histogram
- Geolocation
- Raster reprojection
- Georeferencing
- Automatic vectorization
- Band algebra
- Region of Interest (ROI) definition
- Supervised classification
- Semi-supervised classification
- Decision tree
- Transformations
- Image fusion
- Mosaic
- Scatter diagram
- Image profiles

ILWIS

Integrated Land and Water Information System, formerly commercial software, now open source.

• Image enhancement (contrast, linear stretching)
• Filtering
• Band combination and compositing
• Band ratios and indices
• Georeferencing
• Multi-band statistics
• Principal component analysis
• Image arithmetic
• Image fusion (e.g. pan-sharpening)
• Image classification

MicroDEM

A very strong terrain/DEM analysis program, but has other applications as well, including remote sensing.

• Contrast enhancement
• Filters
• Band histograms
• Correlation (covariance) matrix
• Scattergrams
• Band ratios and normalized indices (e.g. NDVI)
• Principal components analysis
• Multi-band merges
• Image training and classification
• Hyperspectral image analysis (AVIRIS)
• Image averaging
• Pan-sharpening

SAGA

Not primarily a remote sensing application, but has some modules for grid manipulation, statistics and analysis that could be useful.

Spring

LANDSAT, SPOT, ERS-1 and NOAA/AVHRR Data input;

Registration and Geometric Correction;

Image Mosaic with gray level equalization;

Image Enhancement by Histogram Manipulation;

Spatial Filtering;

IHS and Principal Components Transformations;

Arithmetical Operations;

Pixel Values Reading;

Maximum-likelihood pixel-based classifier;

Image Segmentation and Region Classifiers (Supervised and Unsupervised);

LANDSAT and SPOT Images Restoration;

Morphological Filters for Images;

Mixture Models;

Markov-based Techniques for Image Post-Classification;

Radar Image Processing.

And if you want to create your own remote sensing analysis program, or add capabilities to a GIS, there’s the Orfeo Toolbox (OTB), an open-source library/API for image processing:

• image access: optimized read/write access for most of remote sensing image formats, meta-data access, simple visualization;
• sensor geometry: sensor models, cartographic projections;
• radiometry: atmospheric corrections, vegetation indices;
• filtering: blurring, denoising, enhancement;
• fusion: image pansharpening;
• feature extraction: interest points, alignments, lines;
• image segmentation: region growing, watershed, level sets;
• classification: K-means, SVM, Markov random fields;
• change detection.

HT to Melaneum in comments.