OSGeo Cartographic Engine

Motivation

There are plans about new cartographic tools (map composer) for QGIS, as well as for GRASS. We suggest to develop a joint library for the various functions which could be shared across GRASS, QGIS and other projects with bindings to Qt, Python etc. The GUI part will be done within the individual software projects.

Functionality

Shared functions may include

• class breaks (various algorithms)
• histogram analysis
• color ramps
• RGB and possibly CYMK support (aka color transformations) etc.
• Algorithms for intelligent label placement
• Symbology management
• map surround
• legend
• cartographic templates (ie. predefined map styles)

Programming Language

• C? C++?

Perhaps we could implement the core in C++, but provide a high level C API for applications and environments wanting to drive the library. C++ is a strong implementation language, but presenting a C API to the outside world reduces complexity calling from other languages or compiler versions and reduces "interface fragility".

• Python bindings?

There has been talk on the GMT mailing list about Python bindings to the core C API. Since GMT already has a wealth of routines for plotting directly to PS|EPS format files, this route may give developers a great head-start. There has been some work on the integration of GRASS and GMT in the past, with several user-submitted modules.

Output Formats

What output formats do we want to target. I think at the core this question comes down to whether we want to render everything to a raster format or whether we wish to preserve linework, and text in non-raster form. That is, whether output output is a raster format, or a raster+vector+text format like postscript/pdf.

If a cartographic product is the objective, I think selection of an output format like PDF makes a lot of sense, but it does make interactive composition more complicated and it is possible we have limited pdf/postscript development expertise in our developer community (the GMT developers may be of help here...).

Existing code to be recycled

There will be code in GRASS, QGIS, the Python Cartographic Library (http://zcologia.org/cartography) and other sources which could be integrated (check license compatibility). Please indicate precisely where to find the source code, license, programming language:

• Label placement code:
  • Mapserver labeling code (MapServer License, C language)
  • GRASS v.label.sa (GPL, C language)
• Color management:
  • MapGuide, CalculateDistribution and Color (LGPL.C++)
  • OpenJump ?
• Stylization:
• Postscript/PDF output:
  • GRASS ps.map (Postscript output) and PS driver
• PNG output:
  • GRASS PNG driver
  • See AGG below
  • Cairo Graphics Library

• Class breaks:
  • GRASS different algorithms for class breaks (GPL, C)

End User Needs

• Print to small format medium (eg 8.5in x 11in, 11in x 14in)
• Interactive layout
• High quality printing
• Storage of cartographic symbolizing
• symbols library
• Seprate cartographic and geographic representation (eg changes to carto does not affect geo)
• Rules based cartography stored in RDBMS (eg series 400 highways are blue with double lines)
• Multiple export formats
  • Geotiff
  • PNG
  • PDF / GeoPDF

Technologies

• AGG (sophisticated rendering of vector/text graphics to raster format - used by MapServer, MapGuide, Mapnik).
• Freetype - text management and rendering library

License

It is proposed to license the OSGeo Cartographic Library under LGPL. The license needs to be GPL compliant.

Interested people

• Markus Neteler (proposer)
• Horst Düster
• Martin Landa
• Marco Hugentobler
• Frank Warmerdam
• Agustin Diez
• Moritz Lennert
• Dave Sampson: End User, Search and Rescue Maps,
• Dylan Beaudette: Soil Science Researcher, OSGeo evangelist