Coordinate Conversion Scripts

Convert between pixel, geographic, and projected coordinate systems using GDAL

The gdal2Coordinates collection provides utilities for converting between different coordinate systems based on the geospatial information embedded in raster files.

Overview

These scripts read the coordinate system and geotransformation matrix from a GDAL-supported raster file to perform coordinate transformations. All conversions use the projection information from the input image.

Available Scripts

pixel2longlat.py

Converts pixel coordinates to latitude/longitude (geographic) coordinates.

sample · float · required

The pixel/sample position (column number)

line · float · required

The line position (row number)

infile · string · required

Path to the input raster file

Usage:

python pixel2longlat.py sample line infile

Example:

python pixel2longlat.py 100 200 terrain.tif

Output:

pixel: 100          line: 200
longitude: -112.456789      latitude: 35.123456
longitude: 112d27'24.44"W   latitude: 35d7'24.44"N

The script calculates coordinates for the center of the specified pixel by applying a half-pixel shift.

pixel2meters.py

Converts pixel coordinates to projected coordinates in meters (or feet, depending on the projection).

sample · float · required

The pixel/sample position (column number)

line · float · required

The line position (row number)

infile · string · required

Path to the input raster file

Usage:

python pixel2meters.py sample line infile

Example:

python pixel2meters.py 500 750 projected_dem.tif

Output:

pixel: 500          line: 750
X: 445678.500000    Y: 3789234.500000

longlat2meters.py

Converts longitude/latitude coordinates to projected coordinates (X, Y) in meters or feet.

longitude · float · required

Longitude in decimal degrees

latitude · float · required

Latitude in decimal degrees

infile · string · required

Path to the input raster file (provides projection information)

Usage:

python longlat2meters.py longitude latitude infile

Example:

python longlat2meters.py -112.5 35.2 projected_map.tif

Output:

longitude: -112.500000      latitude: 35.200000
X: 450000.000000            Y: 3900000.000000

meters2longlat.py

Converts projected coordinates (X, Y) in meters or feet to longitude/latitude.

X · float · required

X coordinate in meters (or feet)

Y · float · required

Y coordinate in meters (or feet)

infile · string · required

Path to the input raster file (provides projection information)

Usage:

python meters2longlat.py X Y infile

Example:

python meters2longlat.py 450000 3900000 projected_map.tif

Output:

X: 450000.000000            Y: 3900000.000000
longitude: -112.500000      latitude: 35.200000
longitude: 112d30'0.00"W    latitude: 35d12'0.00"N

Implementation Details

Coordinate Transformation Process

All scripts follow a similar workflow:

1. Open the input raster

   Use GDAL to open the raster file in read-only mode

2. Read geotransformation matrix

   Extract the affine transformation coefficients that map between pixel and ground coordinates

3. Create spatial reference objects

   Build OGR spatial reference objects from the raster’s projection information

4. Transform coordinates

   Apply the appropriate transformation using GDAL/OGR coordinate transformation functions

5. Apply pixel center offset (where applicable)

   Shift coordinates to represent the center of pixels rather than corners

Geotransformation Matrix

GDAL uses a 6-coefficient affine transformation:

X = geomatrix[0] + geomatrix[1] * pixel + geomatrix[2] * line
Y = geomatrix[3] + geomatrix[4] * pixel + geomatrix[5] * line

Where:

• geomatrix[0]: Top-left X coordinate
• geomatrix[1]: Pixel width (X resolution)
• geomatrix[2]: Row rotation (typically 0)
• geomatrix[3]: Top-left Y coordinate
• geomatrix[4]: Column rotation (typically 0)
• geomatrix[5]: Pixel height (Y resolution, typically negative)

Requirements

Python 2/3

pip install gdal

conda install gdal

The scripts support both old and new GDAL Python bindings:

• Modern: from osgeo import gdal, osr
• Legacy: import gdal (automatically detected)

Use Cases

Interactive Mapping

Convert mouse clicks on images to geographic coordinates for display

Data Integration

Transform coordinates between datasets with different projections

Ground Control

Identify ground coordinates for surveyed pixel locations

Quality Control

Verify georeferencing accuracy at known control points

Credits

Based on tolatlong.py by Andrey Kiselev ([e-mail]). Extended for meter/feet conversions by Trent Hare (USGS).

These scripts are part of the GDAL Python samples and are released under the MIT License.