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Wikipedia:Graphics Lab/Resources/QGIS/Reprojection: Difference between revisions

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{{in progress|—Contribute to this tutorial by completing one section welcome !}}▼
{{stub}}
▲{{in progress|—Contribute to this tutorial by completing one section welcome !}}
 
== Projection (0%) ==
:{{waiting}} → waiting a volunteer
:{{in progress}}
[[File:Equirectangular projection SW.jpg|300px|thumb|Equirectangular projection of the world; the standard parallel is the equator (plate carrée projection).]]
* [http://forum.qgis.org/viewtopic.php?f=2&t=8712 Raster layer to Robinson]
[[Image:Tissot indicatrix world map equirectangular proj.svg|thumb|right|300px|The equirectangular projection with [[Tissot's indicatrix]] of deformation]]
Work for both ETOPO1 (world file), small SRTM tile, and merged tiles.
[[File:Winkel triple projection SW.jpg|thumb|right|300px|[[Winkel tripel projection]], lowest balance of distortion, used by the [[National Geographic]].]]
[[File:Tissot indicatrix world map Winkel Tripel proj.svg|thumb|right|300px|The Winkel tripel projection with [[Tissot's indicatrix]] of deformation.]]
;Background
QGIS display your data using the projection you tell it to use. By default, the lat/long projection (= [[Equirectangular projection]], example aside) is used, code: {{green|'''WGS84 lat/lon (EPSG:4326)'''}}. This projection is the most convenient for georeferencing, but imply strong distortions at polar latitudes. You may be interested to set a projection when you start a project, or to reproject (warp) an existing lat/long project to a specific projection just before to export your final image or svg. Indeed, each country often have a specific conventional projection to minimized distortions of its geographic space.
 
;Source projection
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;Reproject a vector layer
{{stub}}
;Frequent projections
 
{{main|List of National Coordinate Reference Systems}}
== Raster to Vector (polygons) (0%) ==
{{in progress|→ Yug}}
* [http://forum.qgis.org/viewtopic.php?f=2&t=8752 Covert to vector]
* [http://forum.qgis.org/viewtopic.php?f=2&t=7396 Edit polygons]
* [http://www.gdal.org/gdal_contour.html Gdal_contour] ([http://georezo.net/wiki/main/logiciels/gdal/couteau_suisse/gdal_contour fr])
* [http://tavmjong.free.fr/INKSCAPE/MANUAL/html_fr/Trace.html Using TheGIMP (fr)]
'''Concept:''' Use an elevation GIS file, a discrete black & white colormap, and the Print composer to output one 1500px/1500px black & white png for each altitude (0m, +200m, +500m, etc, name the png accordingly!). This by a cycle such as 1. editing the map color, 2. actualizing the Print composer, 3. outputting the new png. Then use Inkscape to vectorize : load all png, align them, vectorize each using 2 colors + delete background. Color each vector polygon level (0m, 200m, ...) as need.<br />
;Introduction
QGis don't convert raster polygons into vector polygons. It does contours, but which have no fill, and thus, are not suitable.
;QGis cycles
;Inkscape cycles
 
== Add a plugin (100%) ==
:{{in progress|— concept ok, screenshot welcome (Fetch python plugins' window).}}
;Plugin in the repositories
Most plugin are in the repositories.
# QGis > Plugins > Fetch python plugins (a window pop up)
# > tab "Repositories" > Add 3rd party repositories > ok.
# > tab "Plugins" > Filter: [YourKeyWord] > (if you see your plugin: click) > Install plugin
Our important plugins: Shaded relief ; SimpleSvg,
 
;Plugin not in the repository
{{summarization|1=
:''This section is about adding a plugin '''not''' available through QGis (1.7) > Plugins > Fetch plugins, and thus to install handily. We take the case of QGis SimpleSVG plugin.''
 
# Download the plugin > Unzip it.
# Cut-Paste the folder in
#: for Linux : in /home/YOURUSERNAME/.qgis/python/plugins/ (paste me here!)
#: for Windows: somewhere in c:/documents and settings, within the QGis' python plugins folder.
# QGis (1.7) > Plugins > Manage plugins > QGis Plugins Manager (pop up)¹ > search key word (SVG) > check the good plugin + ok
# >> Open a/some vector layers or a project with them >
# >> Plugins > Find your plugin: "Save as SVG" > Save as SVG > Choice your ouput place.
:¹: this window also provide you the address of '''your''' plugin directory !
 
SimpleSVG currently save the QGis' screen as a SVG '''with the correct layer division'''. This save us a lot a energy for later [[Inkscape]] work, especially colorations.
SimpleSVG is a plugin currently under developement, Richard Duivenvoorde is looking for ideas for improvement.
}}
 
== Links ==
* [[Liste of National Coordinate Reference Systems]]
== References ==
<references />
{{Digital cartography tutorials}}
 
{{summarizationCollapse|title=|1=
== (I should read before writing) ==
Read:
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# http://www.qgis.org/wiki/Users_Corner
# [[:En:User:Captain_Blood/GMT_Example]]
{{[[:fr:Wikipédia:Atelier graphique/Didacticiels cartographiques/Didacticiels pour la cartographie numérique géoréférencée}}]]
 
Travaux impressionnant:
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