
MARBLE - MANIFESTO 

Principles and intentions of the Marble Project


v.0.3.2, April 12th, 2007


Virtual Globes have existed since decades already and have been
subject of numerous papers in scientific research.  Although many of
them had been available for personal computers they only recently
gained the awareness of public interest: Google Earth suddenly allowed
people to spot their houses' roofs free of charge from high above and
enabled them in combination with Google Maps to show their Google
Search Queries referenced on a geographical map.  Almost instantly
Google Earth had become the "industry leader" among virtual globes
that others had to measure up to [1].


Why Marble?
===========

Today there exist numerous virtual globes and the market has embraced
strong contenders such as Google Earth/Maps, MS Virtual Earth 3D and
NASA WorldWind [2]. A new virtual globe project must be able to offer
strong selling points and has got to focus on those without
compromises. Otherwise it simply won't gain public relevance.

"Where?" is a pretty basic question that computer users have got to
ask and answer quite often - no matter what they are working on.  The
free desktop has been advancing since years already.  And while
there's a pretty large amount of free software GIS ("Geographical
Information System") applications available [3] they are mostly
targeted at advanced users who deal with geo data during their daytime
jobs or as a matter of enthusiasm.  However, most people out there
aren't cartographers and don't want to be.  These people expect a
simple and clean task-oriented interface that adheres to the map
layout standards that decades of cartography have developed to improve
ease of use of maps.

So for casual users there is still missing a fast, flexible, visually
pleasing and easy to use map component.  For developers, Marble offers
a light-weight, fast, cross platform map component that can be used
online as well as offline with meaningful results and that don't
require proprietary webservices.

Marble is meant to become for "geo browsers" what KHTML/WebKit is for
web browsers already.

From an average user's point of view a map component such as "Marble"
should meet the following requirements:

1.  FAST: 

    To allow instant access and usage as a widget the Marble Widget
    should start up instantly and be ready for use within 2-3
    seconds.  So "application" startup time should always be kept as
    low as possible.

    Technically this means that the Marble Widget needs to be heavily
    optimized for start up times and should have a minimal number of
    dependencies (as an increasing amount of libraries will slow down
    the application's launch).

    Most other virtual globes have startup times of 15-30 secs.
    That's just an eternity to wait for if you just want to look up
    something.


2.  VISUALLY APPEALING: 

    The maps drawn by Marble Widget should adhere to visual
    cartographic standards and should look appealing.  Usually people
    prefer the 3D globe view as it looks more natural, mostly because
    of minimal distortion and because it looks more "advanced". It
    should be possible to easily print the maps and to embed them into
    documents without getting a pixel mess that is hard to decipher.

    Most other virtual globes don't offer good printing support and
    the graphical representation most of the time is just limited to
    satellite views that are often labeled pretty badly. Web based
    solutions (such as Google Maps) are quite static in their
    appearance and are limited in terms of possible modification.


3.  EASE OF USE: 

    Another very important aspect is usability: The feature set should
    cover the use cases of the primary target user only.  3D flights
    are pretty exciting for users that want to be entertained.
    However most users don't need them, don't have the time to
    experiment with them or don't even discover that feature.  So
    focusing on the top-bottom view exclusively ("2.5D") makes sense
    for Marble.

    Maps should be easy to read.  In a lot of cases this will mean
    that the flat projection ("equirectangular projection" / "plate
    carrée") is more convenient (e.g. in a timezone chooser dialog).

    I personally consider Google Earth's interface too complex for
    most users we are aiming for.  Google Maps on the other hand seems
    too simple to me and also has a slight annoyance factor due to its
    web based nature.


4.  MINIMAL HARDWARE/SOFTWARE REQUIREMENTS:

    The Marble Widget should work at usable speed out of the box on
    all possible hardware the desktop environment is running on.  It
    should always show exactly the same output independent of the
    hardware.  During installation modifications to the system should
    stay as low as possible.

    This is an important point as people will simply neglect a
    solution if it's too painful to install or results in other
    unnecessary challenges during configuration.  Unfortunately many,
    if not most, computer systems out there don't offer decent 3D
    hardware acceleration for graphics.  So the solution we are aiming
    for should not depend on 3D hardware acceleration, although we
    certainly might want to offer solutions such as an OpenGL backend
    as an option.  Also the amount of software needed to install the
    map component should stay as low as possible (see 1.) ).


5.  OFFLINE USAGE: 

    The Marble Widget should offer a minimal data set that is
    specifically edited and compiled for offline usage.  This is
    especially useful in countries where internet access is restricted
    or expensive.  Online usage should cover incremental downloading
    of texture tiles, vector data (e.g. OpenStreetMap) and wikipedia
    articles.
    Concerning offline geographical data Marble intends to deliver the 
    "biggest bang for the byte" and provide as much high quality 
    information per byte as possible.

    For all information that goes beyond map labels ("Marble Almanac")
    we have started cooperation with the Wikipedia Offline Reader
    Project.


6.  FREE SOFTWARE & OPEN STANDARDS: 

    The Marble Widget is free software and should use a small set of
    open standards for communication with other applications at
    runtime and to save data to the storage medium.  The open KML file
    format[4] used by Google Earth is probably the most popular file
    format these days to geo reference data.  Through "feeding" KML
    streams to the map component, applications are offered a simple
    "programming" interface to control the map's appearance and
    behaviour.  All Information displayed on the map widget should be
    covered by free licenses using sources such as NASA or
    OpenStreetMap.

    Many other virtual globes are proprietary and are using commercial
    geo data that is considered "non-free" (as it isn't freely
    redistributable).


The Marble Universe
===================

Apart from the Marble Widget (which is implemented using the Qt4.2
library only) there are other planned member components of the Marble
universe:

1. "Marble Desktop Globe": 

    KDE 4 application for KDE-EDU: This "reference" application is
    meant to show off much of Marble's full potential.  At the current
    point of time it's the next logical step as educational
    applications don't need to cover the data in full detail to be
    useful.  Once it reaches maturity the Marble backend could be
    moved into a more central place, e.g. kdelibs/base.

2. "Marble Widget":

    Can be used in different applications like KStars, KControl,
    DigiKam, KGeography, Kopete, Addressbook, Risk-Game, KWorldClock,
    Traceroute, Plasma Weather Applet, and so on. Depending on the use case
    it can have different appearances:
     - "normal" widget
     - selection dialog
     - developer mode

3. "Marble Framework":

    A framework of geo services for the desktop. This should cover a
    "position provider" backend like GPS, hostip.info, track turtle,
    and information services ( "Marble Almanac" ).


Torsten Rahn


References:

[1] as an interesting read see the discussion section at
    http://www.earthslot.org/vgconference/VGconference_results.php

[2] for a nice introduction into virtual globes and a
    non-comprehensive list of them see the article at Wikipedia
    http://en.wikipedia.org/wiki/Virtual_Globe

[3] www.freegis.org provides a nice software overview on Free
    Geographic Information Systems

[4] KML 2.1 Reference available at:
    http://earth.google.com/kml/kml_tags_21.html
