How to use the command `gdalinfo` (with examples)

gdalinfo is a versatile command-line utility from the Geospatial Data Abstraction Library (GDAL) that provides valuable information about raster datasets. This tool can return extensive metadata on GDAL-supported raster file formats, making it a crucial resource for geospatial analysts and developers working with raster data. Whether you’re determining raster dimensions, coordinate systems, or get an overview of image statistics, gdalinfo can efficiently extract this information.

Use case 1: List all supported raster formats

Code:

gdalinfo --formats

Motivation:

Understanding which raster formats are supported by GDAL is essential for anyone working within the geospatial field, as it ensures compatibility when processing and manipulating geospatial data. Knowing the available formats can help facilitate workflows that involve converting between different raster types.

Explanation:

• --formats: This argument prompts gdalinfo to list all raster formats that GDAL can read and write. It’s a valuable feature for checking the breadth of data file types GDAL can handle and ensures that the user can plan for format handling and conversion.

Example output:

Supported Formats:
  VRT -raster (rw+v): Virtual Raster
  GTiff -raster (rw+v): GeoTIFF
  HFA -raster (rw+v): Erdas Imagine Images (.img)
  ...

Use case 2: List information about a specific raster dataset

Code:

gdalinfo path/to/input.tif

Motivation:

Analyzing specific file metadata is often necessary for geospatial professionals who need to understand the characteristics of their raster data before further processing. This might include confirming resolution, spatial extent, coordinate reference system, and other pertinent details.

Explanation:

• path/to/input.tif: This is the input raster file whose information you want to extract. Replace path/to/input.tif with the actual path to your file. The command returns comprehensive details about the dataset, including its size, type, number of bands, and metadata tags.

Example output:

Driver: GTiff/GeoTIFF
Files: input.tif
Size is 512, 512
Coordinate System is:
GEOGCS["WGS 84",
    DATUM["WGS_1984",
    ...

Use case 3: List information about a specific raster dataset in JSON format

Code:

gdalinfo -json path/to/input.tif

Motivation:

JSON, or JavaScript Object Notation, is widely used for data interchange due to its lightweight and structured nature. Extracting raster data information in JSON format is beneficial for developers who may want to manipulate or display this information within web applications or other systems that handle JSON data.

Explanation:

• -json: Requests the output to be formatted in JSON, providing structured output that can easily be manipulated programmatically.
• path/to/input.tif: The path to the input file that is being interrogated.

Example output:

{
    "driver": "GTiff",
    "files": ["input.tif"],
    "size": [512, 512],
    "coordinateSystem": {...}
}

Use case 4: Show histogram values of a specific raster dataset

Code:

gdalinfo -hist path/to/input.tif

Motivation:

Histograms offer a graphical representation of the distribution of data values in a raster image. By computing these statistics, users can better understand the range and frequency of specific pixel values, which is critical for image processing tasks such as enhancement or classification.

Explanation:

• -hist: This flag requests gdalinfo to generate a histogram of the raster’s pixel values. Useful for examining value distribution efficiently.
• path/to/input.tif: Specifies the input raster file from which histogram data is retrieved.

Example output:

Band 1 Block=512x512 Type=Byte, ColorInterp=Gray
  Min=0.000 Max=255.000 
  Minimum=0.000, Maximum=255.000, Mean=123.456, StdDev=78.901
  256 buckets from 0 to 255:
  0   1   2   ... 254 255 
  ...

Use case 5: List information about a Web Map Service (WMS)

Code:

gdalinfo WMS:https://services.meggsimum.de/geoserver/ows

Motivation:

Web Map Services (WMS) allow users to access remotely stored geospatial data over the internet. Extracting data about a WMS gives information about available layers and services, thus enabling efficient querying and usage in various GIS applications.

Explanation:

• WMS:: Specifies the protocol prefix to indicate a WMS service is being queried.
• https://services.meggsimum.de/geoserver/ows: The URL endpoint of the WMS service being interrogated, providing remote layer information.

Example output:

WMS Driver:
    Description: WMS
    Services URL: https://services.meggsimum.de/geoserver/ows
    Layers: ...

Use case 6: List information about a specific dataset of a Web Map Service (WMS)

Code:

gdalinfo WMS:https://services.meggsimum.de/geoserver/ows -sd 4

Motivation:

Some WMS provide multiple layers of data. Querying a specific dataset layer helps users focus on the data they need without retrieving unnecessary information, which can improve efficiency and understanding of available spatial data resources.

Explanation:

• WMS: Indicates the service type as a Web Map Service.
• https://services.meggsimum.de/geoserver/ows: The URL of the WMS service from which layer information is extracted.
• -sd 4: Specifies which sub-dataset (layer) to retrieve information from, in this case, the fourth dataset.

Example output:

Subdataset 4:
  Name: ...
  Description: ...

Conclusion:

gdalinfo is an indispensable tool for geospatial data processing, offering detailed information across various formats and services. From diagnosing raster files to exploring remote WMS endpoints, gdalinfo supports a wide array of tasks that cater to both the technical and operational facets of geospatial data management, aiding users in effective data utilization and analysis.