Wikipedia:Graphics Lab/Resources/QGIS/Reprojection

 —Contribute to this tutorial by completing one section welcome !

Add a plugin (100%)

 — concept ok, screenshot welcome (Fetch python plugins' window).

Plugin in the repositories

Most plugin are in the repositories.

1. QGis > Plugins > Fetch python plugins (a window pop up)
2. > tab "Repositories" > Add 3rd party repositories > ok.
3. > tab "Plugins" > Filter: [YourKeyWord] > (if you see your plugin: click) > Install plugin

Our important plugins: Shaded relief ; SimpleSvg,

Plugin not in the repository

Extended content

: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.

Export GIS Vectors & Raster layers to SVG (100%)

 Done - Done, awaiting testing & your feedbacks !

Install the QGIS plugin named "SVGsimple" from the QGIS repository then you can export GIS layers, with both SVG and raster layers, and with a cleanly coded SVG file.

Which information as item name ?

SVGsimple don't natively know which information should be used to name each group or vector item. You have to tell him:

QGIS (1.7) > right-click on a layer > Properties > tab "Labels" > check on "Display label" > Field containing labels > (choice your field, likely 'Name').

Check off "Display label"

SVGsimple will remember the field 'Name' and names the GIS items as such in the SVG. In example the GIS item with the fied 'name' being 'Amazon river' in QGIS will now become the .xml/.svg item 'Amazon river' in Inkscape.

Export as SVG

QGIS (1.7) > Plugins > Save as SVG > Save as SVG > Choice the pathway > Save > ok.

An clean .svg is produced, with both the raster and vector layers. It is now up to you and Inkscape to change the style of each group / item, and and further content (icons, labels, legend, etc.)

Raster to Vector (polygons) (0%)

C → waiting a volunteer

• Covert to vector
• Edit polygons
• Gdal_contour (fr)
• 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.

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

Projection (0%)

C → waiting a volunteer

• Raster layer to Robinson

Equirectangular projection of the world; the standard parallel is the equator (plate carrée projection).

The equirectangular projection with Tissot's indicatrix of deformation

Winkel tripel projection, lowest balance of distortion, used by the National Geographic.

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: 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

First, you have to find the definition of your source projection/file. It's a kind of long equation which definite the properties of each projection. So:

QGis (1.7) > (double click on the layer to reproject) > Layer's properties (window pop up) > tab 'Coordinates Reference System (CRS)' > Layer Spatial Reference System : [projection's definition] > (copy it)

 In progress Which new projection for my map ?

Secondly, you have to choice your target projection.

 In progressTarget projection

Third, you have to find the definition of this target projection.

QGis (1.7) > File > Project's properties (a window pop up) > tab 'Coordinates Reference System (CRS)'

>> Select your target projection* > copy the definition (the long equation) >

>> ?create a personalized projection.?

QGis (1.7) > Raster > Warp (reproject) > (a window pop up)

> fill the fields witht he source SRS, and the target SRS > open in canvas > run > get the result.

Reproject a raster layer

Reproject a vector layer

National Geographic Society et le National Geographic préfèrent aujourd'hui la. Pour une carte de la France métropolitaine, la projection officielle est la Lambert-93 .

Frequent projections

• QGIS default, lat/long, world: WGS84 lat/lon (EPSG:4326)
• National Geographic, Winkel tripel projection, world:
• USA, standard:
• France (metropole), Lambert-93, standard: WGS84 Lambert-93 (EPSG:2154) id:145
• China, Lambert Conformal Conic:

Links

The table above has links to various tutorials and resources which can help in the creation of Wikipedia maps from digital georeferenced data (GIS).

== (I should read before writing) == Read: /Didacticiel d'installation de winGRASS GIS http://www.qgis.org/wiki/Users_Corner En:User:Captain_Blood/GMT_Example Travaux impressionnant: Ombre: SRTM3 v.2 + en:3DEM Geocoded File:China edcp location map.svg, part of the +500 Location maps. Geocoded File:China edcp relief location map.jpg (with paralleles and lattitudes)