Coordinate Conversion Scripts

Tools for converting between pixel, meter, and geographic coordinate systems

Coordinate Conversion Scripts

These utilities convert coordinates between pixel space, projected meters, and geographic (longitude/latitude) coordinate systems using GDAL’s transformation capabilities.

pixel2longlat.py

Converts pixel coordinates to longitude/latitude coordinates.

Usage

python pixel2longlat.py sample line infile

Parameters

sample · float · required

Pixel sample (column) coordinate

line · float · required

Pixel line (row) coordinate

infile · string · required

Input georeferenced image file

Return Values

Outputs to stdout:

• Pixel coordinates (sample, line)
• Longitude and latitude in decimal degrees
• Longitude and latitude in DMS (Degrees, Minutes, Seconds) format

How It Works

1. Reads the geotransformation matrix from the input file
2. Calculates ground coordinates for the pixel center
3. Transforms projected coordinates to geographic (lat/long)
4. Reports results in both decimal and DMS formats

Example

python pixel2longlat.py 1000 500 input_image.tif

Output:

pixel: 1000         line: 500
longitude: -122.456789    latitude: 37.789012
longitude: 122d27'24.44"W    latitude: 37d47'20.44"N

Notes

• Coordinates are calculated for the center of the pixel
• Input file must have valid geotransform and projection information
• Works with any GDAL-supported georeferenced format

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pixel2meters.py

Converts pixel coordinates to X,Y coordinates in the image’s projected coordinate system (typically meters or feet).

Usage

python pixel2meters.py sample line infile

Parameters

sample · float · required

Pixel sample (column) coordinate

line · float · required

Pixel line (row) coordinate

infile · string · required

Input georeferenced image file

Return Values

Outputs to stdout:

• Pixel coordinates (sample, line)
• X and Y coordinates in projected units (typically meters)

Example

python pixel2meters.py 1000 500 input_projected.tif

Output:

pixel: 1000         line: 500
X: 523456.789000    Y: 4567890.123000

Notes

• Returns coordinates in the file’s native projection units
• Does not perform coordinate transformation
• Coordinates are for pixel center

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longlat2meters.py

Converts longitude/latitude coordinates to X,Y projected coordinates based on an input image’s projection.

Usage

python longlat2meters.py long lat infile

Parameters

long · float · required

Longitude in decimal degrees

lat · float · required

Latitude in decimal degrees

infile · string · required

Input georeferenced image defining the projection

Return Values

Outputs to stdout:

• Input longitude and latitude
• Transformed X and Y coordinates in projected units

How It Works

1. Reads projection information from input file
2. Creates coordinate transformation from geographic to projected
3. Transforms the input lon/lat to X/Y meters

Example

python longlat2meters.py -122.4567 37.7890 input_projected.tif

Output:

longitude: -122.456700    latitude: 37.789000
X: 523456.789000    Y: 4567890.123000

Use Cases

• Converting GPS coordinates to map projection
• Preparing coordinates for GIS analysis
• Validating coordinate transformations

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meters2longlat.py

Converts X,Y projected coordinates to longitude/latitude based on an input image’s projection.

Usage

python meters2longlat.py X Y infile

Parameters

X · float · required

X coordinate in projected units (meters or feet)

Y · float · required

Y coordinate in projected units (meters or feet)

infile · string · required

Input georeferenced image defining the projection

Return Values

Outputs to stdout:

• Input X and Y coordinates
• Transformed longitude and latitude in decimal degrees
• Longitude and latitude in DMS format

Example

python meters2longlat.py 523456.789 4567890.123 input_projected.tif

Output:

X: 523456.789000        Y: 4567890.123000
longitude: -122.456700        latitude: 37.789000
longitude: 122d27'24.12"W    latitude: 37d47'20.40"N

Notes

• Performs inverse transformation from projected to geographic
• Useful for converting map coordinates to GPS-compatible format
• Output includes both decimal and DMS formats for convenience

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Common Workflow

These scripts work together for various coordinate conversion workflows:

Workflow 1: Pixel to Geographic

# Direct conversion
python pixel2longlat.py 1000 500 image.tif

# Or two-step conversion
python pixel2meters.py 1000 500 image.tif
# Take X,Y from output
python meters2longlat.py 523456.789 4567890.123 image.tif

Workflow 2: Geographic to Pixel

# Convert geographic to projected first
python longlat2meters.py -122.4567 37.7890 image.tif
# Then use X,Y to find pixel coordinates (requires additional calculation)

Technical Details

Coordinate Systems

All scripts use GDAL/OSR for coordinate transformations:

• Support for any projection defined in the input file
• Automatic handling of datum transformations
• Precise transformation using PROJ library

Pixel Convention

All scripts use pixel center convention:

• Adds half pixel offset to ensure center point
• Consistent with most GIS software conventions

Requirements

Dependencies:

• Python 2.7+ or Python 3.x
• GDAL Python bindings (osgeo.gdal, osgeo.osr)
• Input files must have valid geotransform and projection metadata

Troubleshooting

Error: Unable to load PROJ.4 library

Ensure GDAL is properly installed with PROJ support:

gdalinfo --version

Incorrect transformations

Verify the input file has correct projection information:

gdalinfo input_file.tif

Script returns Usage message

Check that all required parameters are provided in the correct order:

• All three arguments must be present
• Numeric values must be valid
• File must exist and be readable

Author

Based on original work by Andrey Kiselev (tolatlong.py), with modifications by Trent Hare (USGS Astrogeology Science Center).