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0004 Principles and intentions of the Marble Project
0007 v.0.3.2, April 12th, 2007
0010 Virtual Globes have existed since decades already and have been
0011 subject of numerous papers in scientific research.  Although many of
0012 them had been available for personal computers they only recently
0013 gained the awareness of public interest: Google Earth suddenly allowed
0014 people to spot their houses' roofs free of charge from high above and
0015 enabled them in combination with Google Maps to show their Google
0016 Search Queries referenced on a geographical map.  Almost instantly
0017 Google Earth had become the "industry leader" among virtual globes
0018 that others had to measure up to [1].
0021 Why Marble?
0022 ===========
0024 Today there exist numerous virtual globes and the market has embraced
0025 strong contenders such as Google Earth/Maps, MS Virtual Earth 3D and
0026 NASA WorldWind [2]. A new virtual globe project must be able to offer
0027 strong selling points and has got to focus on those without
0028 compromises. Otherwise it simply won't gain public relevance.
0030 "Where?" is a pretty basic question that computer users have got to
0031 ask and answer quite often - no matter what they are working on.  The
0032 free desktop has been advancing since years already.  And while
0033 there's a pretty large amount of free software GIS ("Geographical
0034 Information System") applications available [3] they are mostly
0035 targeted at advanced users who deal with geo data during their daytime
0036 jobs or as a matter of enthusiasm.  However, most people out there
0037 aren't cartographers and don't want to be.  These people expect a
0038 simple and clean task-oriented interface that adheres to the map
0039 layout standards that decades of cartography have developed to improve
0040 ease of use of maps.
0042 So for casual users there is still missing a fast, flexible, visually
0043 pleasing and easy to use map component.  For developers, Marble offers
0044 a light-weight, fast, cross platform map component that can be used
0045 online as well as offline with meaningful results and that don't
0046 require proprietary webservices.
0048 Marble is meant to become for "geo browsers" what KHTML/WebKit is for
0049 web browsers already.
0051 From an average user's point of view a map component such as "Marble"
0052 should meet the following requirements:
0054 1.  FAST: 
0056     To allow instant access and usage as a widget the Marble Widget
0057     should start up instantly and be ready for use within 2-3
0058     seconds.  So "application" startup time should always be kept as
0059     low as possible.
0061     Technically this means that the Marble Widget needs to be heavily
0062     optimized for start up times and should have a minimal number of
0063     dependencies (as an increasing amount of libraries will slow down
0064     the application's launch).
0066     Most other virtual globes have startup times of 15-30 secs.
0067     That's just an eternity to wait for if you just want to look up
0068     something.
0073     The maps drawn by Marble Widget should adhere to visual
0074     cartographic standards and should look appealing.  Usually people
0075     prefer the 3D globe view as it looks more natural, mostly because
0076     of minimal distortion and because it looks more "advanced". It
0077     should be possible to easily print the maps and to embed them into
0078     documents without getting a pixel mess that is hard to decipher.
0080     Most other virtual globes don't offer good printing support and
0081     the graphical representation most of the time is just limited to
0082     satellite views that are often labeled pretty badly. Web based
0083     solutions (such as Google Maps) are quite static in their
0084     appearance and are limited in terms of possible modification.
0087 3.  EASE OF USE: 
0089     Another very important aspect is usability: The feature set should
0090     cover the use cases of the primary target user only.  3D flights
0091     are pretty exciting for users that want to be entertained.
0092     However most users don't need them, don't have the time to
0093     experiment with them or don't even discover that feature.  So
0094     focusing on the top-bottom view exclusively ("2.5D") makes sense
0095     for Marble.
0097     Maps should be easy to read.  In a lot of cases this will mean
0098     that the flat projection ("equirectangular projection" / "plate
0099     carrée") is more convenient (e.g. in a timezone chooser dialog).
0101     I personally consider Google Earth's interface too complex for
0102     most users we are aiming for.  Google Maps on the other hand seems
0103     too simple to me and also has a slight annoyance factor due to its
0104     web based nature.
0109     The Marble Widget should work at usable speed out of the box on
0110     all possible hardware the desktop environment is running on.  It
0111     should always show exactly the same output independent of the
0112     hardware.  During installation modifications to the system should
0113     stay as low as possible.
0115     This is an important point as people will simply neglect a
0116     solution if it's too painful to install or results in other
0117     unnecessary challenges during configuration.  Unfortunately many,
0118     if not most, computer systems out there don't offer decent 3D
0119     hardware acceleration for graphics.  So the solution we are aiming
0120     for should not depend on 3D hardware acceleration, although we
0121     certainly might want to offer solutions such as an OpenGL backend
0122     as an option.  Also the amount of software needed to install the
0123     map component should stay as low as possible (see 1.) ).
0126 5.  OFFLINE USAGE: 
0128     The Marble Widget should offer a minimal data set that is
0129     specifically edited and compiled for offline usage.  This is
0130     especially useful in countries where internet access is restricted
0131     or expensive.  Online usage should cover incremental downloading
0132     of texture tiles, vector data (e.g. OpenStreetMap) and wikipedia
0133     articles.
0134     Concerning offline geographical data Marble intends to deliver the 
0135     "biggest bang for the byte" and provide as much high quality 
0136     information per byte as possible.
0138     For all information that goes beyond map labels ("Marble Almanac")
0139     we have started cooperation with the Wikipedia Offline Reader
0140     Project.
0145     The Marble Widget is free software and should use a small set of
0146     open standards for communication with other applications at
0147     runtime and to save data to the storage medium.  The open KML file
0148     format[4] used by Google Earth is probably the most popular file
0149     format these days to geo reference data.  Through "feeding" KML
0150     streams to the map component, applications are offered a simple
0151     "programming" interface to control the map's appearance and
0152     behaviour.  All Information displayed on the map widget should be
0153     covered by free licenses using sources such as NASA or
0154     OpenStreetMap.
0156     Many other virtual globes are proprietary and are using commercial
0157     geo data that is considered "non-free" (as it isn't freely
0158     redistributable).
0161 The Marble Universe
0162 ===================
0164 Apart from the Marble Widget (which is implemented using the Qt4.2
0165 library only) there are other planned member components of the Marble
0166 universe:
0168 1. "Marble Desktop Globe": 
0170     KDE 4 application for KDE-EDU: This "reference" application is
0171     meant to show off much of Marble's full potential.  At the current
0172     point of time it's the next logical step as educational
0173     applications don't need to cover the data in full detail to be
0174     useful.  Once it reaches maturity the Marble backend could be
0175     moved into a more central place, e.g. kdelibs/base.
0177 2. "Marble Widget":
0179     Can be used in different applications like KStars, KControl,
0180     DigiKam, KGeography, Kopete, Addressbook, Risk-Game, KWorldClock,
0181     Traceroute, Plasma Weather Applet, and so on. Depending on the use case
0182     it can have different appearances:
0183      - "normal" widget
0184      - selection dialog
0185      - developer mode
0187 3. "Marble Framework":
0189     A framework of geo services for the desktop. This should cover a
0190     "position provider" backend like GPS, hostip.info, track turtle,
0191     and information services ( "Marble Almanac" ).
0194 Torsten Rahn
0197 References:
0199 [1] as an interesting read see the discussion section at
0200     http://www.earthslot.org/vgconference/VGconference_results.php
0202 [2] for a nice introduction into virtual globes and a
0203     non-comprehensive list of them see the article at Wikipedia
0204     http://en.wikipedia.org/wiki/Virtual_Globe
0206 [3] www.freegis.org provides a nice software overview on Free
0207     Geographic Information Systems
0209 [4] KML 2.1 Reference available at:
0210     http://earth.google.com/kml/kml_tags_21.html