QCT Convert

A C++ implementation of the (unofficial) Quick Chart (.QCT) File Format Specification (v1.03) offering decoding of .qct map files and export to various formats

A small sample of a .png file exported from a .qct file, depicting the famous Ben Nevis, the highest point in the UK. All rights reserved by Ordnance Survey.

Motivation

This project was inspired by the desire to convert a few of Ordnance Survey UK maps that I have from the proprietary .qct format into more widely accessible formats for use in image viewers and GIS software. It provides a multithreaded C++ implementation of the (unofficial) Quick Chart (.QCT) File Format Specification (v1.03) by Craig Shelley.

Features

• QCT File Decoding
  • Multithreaded decoding
  • Decoding of Huffman-Coded tiles
  • Decoding of Run-Length-Encoded (RLE) tiles
  • Decoding of Pixel-Packed tiles
    • Note: Not implemented, as I have yet to I have yet to come across any .qct file with Pixel-Packed tiles. Feel free to open an issue with a sample .qct file for implementation and testing purposes.
• Export Formats
  • Export map boundaries to .kml
  • Export map to .pngusing fpng
  • Export to GeoTIFF using GDAL
• Other
  • Precompiled binaries for Windows, Linux, and macOS
  • QCT3-file decoding
    • Note: QCT3 files are not supported, as they may include encrypted data for Digital Rights Management (DRM). I may add support for these in the future, for the unencrypted portion that is.

Usage

The command-line interface (CLI) provides a straightforward way to decode .qct files and export them to supported formats. A path to the .qct file is required. Optionally, one may export the .qct file to various formats. If no export options are specified, the tool decodes the file and prints its metadata.

CLI

• <path/to/map.qct>: Path to the input .qct file (required)
• --force: To attempt decoding anyways if the metadata is invalid or shows incompatible file

Export Formats

KML

• --export-kml-path <path>: Export map boundaries to a .kml file

GeoTIFF

• --export-geotiff-path <path>: Export georeferenced map to a .tiff (GeoTIFF) file
• --geotiff-georef-method: Specify the georeferencing method for GeoTIFF export:
  • auto: Automatically determine the most suitable georeferencing method. This is the default method.
  • gcp: Use GCPs (Ground Control Points) for georeferencing. This uses all the georeferencing coefficients (incl. higher order) from the .qct file, yielding a more accurate result, when the higher order coefficients are non-zero. Note, not all GIS software support this method and that additional gdalwarp may be required for GIS software compatibility.
  • linear: GDAL GeoTransform using constant and first order polynomial coefficients. If the higher order georeferencing coefficients in the .qct file are zero, this method is sufficient and recommended, as a wide range of GIS software support this method.

PNG

• --export-png-path <path>: Export map image to a .png file

On Windows:

qct-convert.exe <path\to\map.qct> --export-kml-path <path\to\map.kml> --export-geotiff-path <path\to\map.tiff> --export-png-path <path\to\map.png> 

On Linux/macOS:

qct-convert <path/to/map.qct> --export-kml-path <path/to/map.kml> --export-geotiff-path <path/to/map.tiff> --export-png-path <path/to/map.png>

Acknowledgements

This project would not be possible without the incredible work of Craig Shelley and Mark Bryant on the (unofficial) Quick Chart (.QCT) File Format Specification v1.03.