The ogr2ogr command is a powerful tool for converting geospatial vector data between different file formats. Whether you need to convert Shapefiles to GeoPackage, filter features in a GeoJSON, change coordinate reference systems, load data into a PostGIS database, or clip layers in a GeoPackage, ogr2ogr can handle these tasks efficiently. This article provides examples of each use case, along with explanations of the command arguments and their motivations.

Use case 1: Convert a Shapefile into a GeoPackage

Code:

ogr2ogr -f GPKG path/to/output.gpkg path/to/input.shp

Motivation: Converting a Shapefile to a GeoPackage can be useful when you need to use a different file format that supports advanced features, such as multiple geometry types, attribute tables, and spatial indexes. GeoPackage is an open standard format that is widely supported by Geographic Information System (GIS) software.

Explanation:

• The -f GPKG argument specifies the output file format as GeoPackage.
• path/to/output.gpkg is the path where the converted GeoPackage will be saved.
• path/to/input.shp is the path to the input Shapefile.

Example Output: The Shapefile located at path/to/input.shp will be converted to a GeoPackage file located at path/to/output.gpkg.

Use case 2: Reduce a GeoJSON to features matching a condition

Code:

ogr2ogr -where 'myProperty > 42' -f GeoJSON path/to/output.geojson path/to/input.geojson

Motivation: When working with large GeoJSON files, it can be helpful to filter out features that do not meet specific criteria. This can reduce the file size and improve processing performance. The -where argument allows you to specify the filtering condition based on attribute values.

Explanation:

• The -where 'myProperty > 42' argument specifies the condition for feature reduction. In this example, it filters features where the attribute ‘myProperty’ is greater than 42.
• The -f GeoJSON argument specifies the output file format as GeoJSON.
• path/to/output.geojson is the path where the reduced GeoJSON file will be saved.
• path/to/input.geojson is the path to the input GeoJSON file.

Example Output: The GeoJSON file located at path/to/input.geojson will be reduced to include only features where the attribute ‘myProperty’ is greater than 42. The resulting GeoJSON file will be saved at path/to/output.geojson.

Use case 3: Change coordinate reference system of a GeoPackage from EPSG:4326 to EPSG:3857

Code:

ogr2ogr -s_srs EPSG:4326 -t_srs EPSG:3857 -f GPKG path/to/output.gpkg path/to/input.gpkg

Motivation: Changing the coordinate reference system (CRS) of a GeoPackage can be necessary when working with data that is in a different CRS, or when the projection needs to be modified for a specific use case. In this example, we convert a Geopackage from EPSG:4326 (WGS84) to EPSG:3857 (Web Mercator).

Explanation:

• The -s_srs EPSG:4326 argument specifies the source CRS as EPSG:4326.
• The -t_srs EPSG:3857 argument specifies the target CRS as EPSG:3857.
• The -f GPKG argument specifies the output file format as GeoPackage.
• path/to/output.gpkg is the path where the converted GeoPackage will be saved.
• path/to/input.gpkg is the path to the input GeoPackage.

Example Output: The GeoPackage located at path/to/input.gpkg will be converted, changing its coordinate reference system from EPSG:4326 to EPSG:3857. The resulting GeoPackage will be saved at path/to/output.gpkg.

Use case 4: Convert a CSV file into a GeoPackage, specifying the names of the coordinate columns and assigning a coordinate reference system

Code:

ogr2ogr -f GPKG path/to/output.gpkg path/to/input.csv -oo X_POSSIBLE_NAMES=longitude -oo Y_POSSIBLE_NAMES=latitude -a_srs EPSG:4326

Motivation: Converting CSV files containing geospatial data to a standardized format like GeoPackage allows for better visualization, analysis, and interoperability with other GIS software. This example demonstrates how to specify the names of the coordinate columns in the CSV file and assign a coordinate reference system (CRS).

Explanation:

• -f GPKG specifies the output file format as GeoPackage.
• path/to/output.gpkg is the path where the converted GeoPackage will be saved.
• path/to/input.csv is the path to the input CSV file.
• -oo X_POSSIBLE_NAMES=longitude and -oo Y_POSSIBLE_NAMES=latitude specify the column names in the CSV file that contain the X and Y coordinates respectively.
• -a_srs EPSG:4326 assigns the coordinate reference system (CRS) as EPSG:4326 (WGS84) to the output GeoPackage.

Example Output: The CSV file located at path/to/input.csv will be converted to a GeoPackage file located at path/to/output.gpkg, with the coordinate columns ’longitude’ and ’latitude’. The GeoPackage will have the coordinate reference system (CRS) set to EPSG:4326.

Use case 5: Load a GeoPackage into a PostGIS database

Code:

ogr2ogr -f PostgreSQL PG:dbname="database_name" path/to/input.gpkg

Motivation: Loading a GeoPackage into a PostGIS database allows for advanced spatial querying and analysis capabilities, as well as seamless integration with other spatial data sources. In this example, we load a GeoPackage file into a PostGIS database named “database_name”.

Explanation:

• -f PostgreSQL specifies the output file format as PostgreSQL.
• PG:dbname="database_name" is the connection string to the PostGIS database with the specified database name.
• path/to/input.gpkg is the path to the GeoPackage file that will be loaded into the PostGIS database.

Example Output: The GeoPackage file located at path/to/input.gpkg will be loaded into the PostGIS database named “database_name”.

Use case 6: Clip layers of a GeoPackage file to the given bounding box

Code:

ogr2ogr -spat min_x min_y max_x max_y -f GPKG path/to/output.gpkg path/to/input.gpkg

Motivation: Clipping layers in a GeoPackage file to a specific bounding box can be useful when you need to extract only the features that fall within a certain area of interest. This can be particularly valuable when dealing with large datasets or when you want to focus on a specific region.

Explanation:

• -spat min_x min_y max_x max_y specifies the bounding box coordinates that define the clipping extent.
• -f GPKG specifies the output file format as GeoPackage.
• path/to/output.gpkg is the path where the clipped GeoPackage file will be saved.
• path/to/input.gpkg is the path to the input GeoPackage file.

Example Output: The layers in the GeoPackage file located at path/to/input.gpkg will be clipped to the given bounding box coordinates. The resulting GeoPackage file will be saved at path/to/output.gpkg.

Conclusion:

The ogr2ogr command is a versatile tool for converting, filtering, and manipulating geospatial vector data. With the examples provided in this article, you can now leverage ogr2ogr for various use cases, ranging from format conversion and data reduction to coordinate system transformation and database integration. Experiment with these examples and adapt them to your specific requirements to get the most out of ogr2ogr.