Getting Started with GDAL – A Beginner’s Guide to Geospatial Data
Introduction
If you’ve ever worked with geospatial data or are stepping into the world of GIS, you’ll come across GDAL (Geospatial Data Abstraction Library) sooner or later. GDAL is a powerful, open-source tool that supports a multitude of raster and vector data formats. This guide will help beginners navigate GDAL's essentials, from installation to performing basic geospatial operations.
What is GDAL?
GDAL is a translator library for raster and vector geospatial data formats. It allows users to process, analyze, and convert geospatial datasets efficiently. Whether you’re working on environmental analysis, urban planning, or remote sensing, GDAL is a must-have tool.
Why Use GDAL?
- Supports over 100 raster and vector formats.
- Ideal for automating geospatial data processing.
- Compatible with Python, making scripting straightforward.
- Widely used in open-source GIS software like QGIS.
Setting Up GDAL
Installing GDAL
- Windows: Download the installer from OSGeo4W and select GDAL in the package list.
- macOS: via Homebrew.
brew install gdal
- Linux: Install using the package manager:
sudo apt-get install gdal-bin
- Python Users: Install via pip:
pip install gdal
Essential GDAL Commands
- Extract Metadata: View raster information:
gdalinfo input.tif
- Reproject Raster Data: Reproject a raster to EPSG:4326:
gdalwarp -t_srs EPSG:4326 input.tif output.tif
- Extract Band: Extract a specific band from a multi-band raster:
gdal_translate -b 1 input.tif output_band1.tif
- Convert Raster Formats: Convert a TIFF to PNG:
gdal_translate input.tif output.png
- Clip Raster: Crop raster using bounding box:
gdal_translate -projwin ulx uly lrx lry input.tif output.tif
- Merge Rasters: Combine multiple raster files into one:
gdal_merge.py -o output.tif input1.tif input2.tif
- Resample Raster: Change the resolution of a raster file:
gdalwarp -tr xres yres input.tif output.tif
- Calculate Statistics: Compute statistics for a raster:
gdalinfo -stats input.tif
- Translate to GeoTIFF: Convert a raster to GeoTIFF format:
gdal_translate -of GTiff input.tif output.tif
- Polygonize Raster: Convert raster data to vector polygons:
gdal_polygonize.py input.tif -f "ESRI Shapefile" output.shp
- Generate Overviews: Create pyramid layers for faster display:
gdaladdo -r average input.tif 2 4 8 16
- Warp to Cutline: Clip raster to a vector boundary:
gdalwarp -cutline boundary.shp -crop_to_cutline input.tif output.tif
- Convert to ASCII Grid: Export raster data as an ASCII grid:
gdal_translate -of AAIGrid input.tif output.asc
- Get NoData Value: View the NoData value of a raster:
gdalinfo -mm input.tif
- Set NoData Value: Assign a NoData value to a raster:
gdalwarp -dstnodata value input.tif output.tif
- Rasterize Vector: Convert vector data into a raster:
gdal_rasterize -a attribute_name -tr xres yres -l layer_name vector.shp output.tif
Scripting with GDAL in Python
GDAL also supports Python scripting for automation. Here’s an example:
from osgeo import gdal
# Open a raster file
raster = gdal.Open("input.tif")
# Get raster metadata
print("Raster Size:", raster.RasterXSize, "x", raster.RasterYSize)
print("Projection:", raster.GetProjection())
# Close the file
raster = None
Resources
- Mastering GDAL Tools (Full Course)
- Refer to the GDAL Documentation for detailed guidance.
- A Gentle Introduction to GDAL by Robert Simmon Part-1,Part-2,Part-3,Part-4,Part-5,Part-6,Part-7