On Wed, Dec 31, 2008 at 03:34:08PM +0100, Jacolin wrote: > Hi dev list, > > Here is a rst file for an introduction about OpenLayers. All informations may > not be correct, nor my english. > > As you will see, this document could be a duplicate document with the > spherical mercator doc ... but less complete.
I think that we should not have duplicated information; if we need to include enough code to make something work, then we can do that, but beyond that, we should just link to the spherical mercator doc. (In other words, I don't mind having *reasons* for boilerplate code listed elsewhere.) I definitely dont think that "How to add 900913 to your Map Server" belongs in an intro doc. I'm going to clean this up a bit and then we can see what we think about it. What you have right now is similar to what I have here: http://svn.crschmidt.net/personal/openlayers/doc/getting_started.txt And I think that's a good start. > I would like to know if you (and the community) are interesting to get more > document from me, and if others people are working on such document and which > topic (in order to avoid other duplicate works). > > Best regards, > > Y. > ============ > Introduction > ============ > > .. contents:: > > Presentation > ------------- > OpenLayers is a library written in JavaScript which allow you to develop > easily and quiclky an indepandant map server client interface. It proposes by > default loading data from OGC standards like WMS, WFS, from commercial Map > Base Layer like Google, Yahoo, Virtual Earth, from various data format KML, > GeoRSS, GML, etc. Among features available, you'll find zooming, panning, > displaing data, layer tree, tiled layers and cache client side. TileCache > allow you to cache server sider and will be presented later in this document. > > OpenLayers is developed by an increasingly large community, and you can > contact them via a mailing list or IRC. OpenLayers is a project hosted by > OSGeo. The official site is located at http://openlayers.org. > > You'll find a short documentation in English here: > http://openlayers.org/doc/, the API doc is available here: > http://dev.openlayers.org/docs/files/OpenLayers-js. html and there are a lot > of examples here: http://openlayers.org/dev/doc/examples.html > > *Objectifs of this chapter:* > * Know more about map and layer object ; > * Create your first map ; > * Add your own layer using a commercial base layer. > > Installation > ------------ > > There are two ways to use OpenLayers on its Web site. The first is to call > the library by the JavaScript <script> tag: > > .. code-block:: javascript > > <script src='http://openlayers.org/api/OpenLayers.js'></script> > > Of course you can download the local library from the download page: > http://trac.openlayers.org/wiki/HowToDownload > > There are two presentations from the library. The first, known as sources of > OpenLayers, consists of a file openlayers.js which calls all other files > included in the tree of the library. The second version, a version built, but > not in binary format, consists of building all the files into a single > compressed file. The file size is small, but code is unreadable: any > unnecessary space is removed during compression. The call for the library is > made by the same way, but with reference to the page where it is called: > > .. code-block:: javascript > > <script src='api/OpenLayers.js'></script> > > You are now ready to use the library. > > My first map > ------------ > The OpenLayers API uses mainly two objects this is not exactly true, but > enougth for beginning): the //map// and //layers// objects. A Map object > stores information on the map, its size, projection units, its scope, and so > on. In a map, the data is displayed in the form of layers (//layers//). A > //layers// object is a data source that defines how OpenLayers must recover > the data and display them. > > > Setting > +++++++ > > Building an OpenLayers interface requires the addition of HTML code in your > page. You can put a map where you want. Here is a simple example for creating > a map with OpenLayers. > > .. code-block:: html > > <html> > <head> > <title>OpenLayers Example</title> > <script > src="http://openlayers.org/api/OpenLayers.js";></script> > </head> > <body> > <div style="width:100%; height:100%" id="map"></div> > </body> > </html> > > To initialize a map in this interface, you must write a few lines of > JavaScript code in the header of the page or in a map.js file for example. > The file or the code should be placed after the insertion of the library > OpenLayers. Generally, it creates a ''init()'' function which, put in the > <body> tag initialize the map after loading the page. > > .. code-block:: javascript > > var map; > function init() { > //creating map object > map = new OpenLayers.Map('map'); > //creating a WMS layer > var wms = new OpenLayers.Layer.WMS( > "http://labs.metacarta.com/wms/vmap0";, > {'layers':'basic'} > ); > //adding wms layer to the map object > map.addLayer(wms); > } > > > Here is a full example: > > .. code-block:: html > > <html> > <head> > <title>OpenLayers Example</title> > <script src="http://openlayers.org/api/OpenLayers.js";></script> > </head> > <body> > <div style="width:100%; height:100%" id="map"></div> > <script defer="defer" type="text/javascript"> > var map = new OpenLayers.Map('map'); > var wms = new OpenLayers.Layer.WMS( "OpenLayers WMS", > "http://labs.metacarta.com/wms/vmap0";, {layers: 'basic'} ); > map.addLayer(wms); > map.zoomToMaxExtent(); > </script> > > </body> > </html> > > > <html> > <script src="http://openlayers.org/api/OpenLayers.js";></script> > <div style="width:400px; height:200px" id="map"></div> > <script defer="defer" type="text/javascript"> > var map = new OpenLayers.Map('map'); > var wms = new OpenLayers.Layer.WMS( "OpenLayers WMS", > "http://labs.metacarta.com/wms/vmap0";, {layers: 'basic'} ); > map.addLayer(wms); > map.zoomToMaxExtent(); > </script> > </html> > > Add Google Maps Layers > ++++++++++++++++++++++ > > Google uses a distorted projection which implies that others layers are not > always overlaid correctly. Google uses a Spherical Mercator projection > assuming that the earth is spherical (which is incorrect). Following this, > for a large zoom a shift appears between the Google map and your data. You > can reproject your data in another projections (see later), or define the > spherial projection within the parameters of the map and set up a parameter > in the Commercial base layer options. Here is the way to enable this in your > map, first define your map options by using the following: > > .. code-block:: javascript > > var options = { > projection: "EPSG:900913", > units: "m", > maxResolution: 156543.0339, > maxExtent: new OpenLayers.Bounds(-20037508.34, -20037508.34, > 20037508.34, 20037508.34) > }; > > > Projection definition for proj4 is following: > > .. code-block:: bash > > +proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=0 > +k=1.0 +units=m +nadgri...@null +no_defs > > More information are available at > [[http://proj.maptools.org/faq.html#sphere_as_wgs84|this page]]. For > GeoServer: > > .. code-block:: bash > 900913=PROJCS["WGS84 / Simple Mercator", GEOGCS["WGS 84", > DATUM["WGS_1984", SPHEROID["WGS_1984", 6378137.0, 298.257223563]], > PRIMEM["Greenwich", 0.0], UNIT["degree", 0.017453292519943295], > AXIS["Longitude", EAST], AXIS["Latitude", NORTH]], > PROJECTION["Mercator_1SP_Google"], > PARAMETER["latitude_of_origin", 0.0], PARAMETER["central_meridian", > 0.0], > PARAMETER["scale_factor", 1.0], PARAMETER["false_easting", 0.0], > PARAMETER["false_northing", 0.0], UNIT["m", 1.0], AXIS["x", EAST], > AXIS["y", NORTH], AUTHORITY["EPSG","900913"]] > > The GeoServer release greater or equal to 1.5.4 doesn't need to add the > projection definition to the configuration, already included in the > configuration file. > > Go back to OpenLayers, to add a Google base layer you have to add a ''layer'' > object to your ''map'' object with the following method: > > .. code-block:: javascript > > new OpenLayers.Layer.Google(LayerName, options); > > > ''options'' parameter is an array of options to be sent to the method. > Available options are (read the OpenLayers API for OpenLayers.Layer.Google to > get more information): > * ''type'' : type of the commercial base layer, google here (normal, > satellite, mixte) ; > * ''sphericalMercator'' : is the projection is sphericalMercator? Set value > to ''true''. > > For the ''type'' parameter, choose one between: > * G_NORMAL_MAP > * G_SATELLITE_MAP > * G_HYBRID_MAP > > You have three constants that you can modify: > * ''MIN_ZOOM_LEVEL'' : default value: 0 ; > * ''MAX_ZOOM_LEVEL'' : default value: 19 ; > * ''RESOLUTIONS'' > > For example: > > .. code-block:: javascript > > var google = new OpenLayers.Layer.Google( > "Google Streets", > {type: G_NORMAL_MAP, 'sphericalMercator': true} > ); > > > .. important:: > > If you enable several type of Google layer (hybrid, default, satellite, for > example), add your layers with the ''addlayers()'' method or you can have a > shift between each Google baselayer. Example: ''map.addLayers ([google, > hybrid, satellite]);'' > > > If you wish to overlay a GML layer (or other) with a commecial baselayer > (like Google), you *must* use the option '' 'sphericalMercator': true'', > moreover you have to reproject your data in the correct projection, like this: > > .. code-block:: bash > > ogr2ogr -f "ESRI Shapefile" -t_srs "+proj=merc +a=6378137 +b=6378137 > +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=0 +k=1.0 +units=m +nadgri...@null > +no_defs" -s_srs "EPSG:4326" Mono2006_2.shp Mono2006_region.shp > > If you are using OGR release greater or equal to 1.5.0, use the 'EPSG:900913' > code directly to reproject your data. > > Finally, for PostGIS this can be useful: > > .. code-block:: sql > > INSERT INTO spatial_ref_sys (srid,auth_name,auth_srid,srtext,proj4text) VALUES > (900913,'EPSG',900913,'PROJCS["Google Mercator", GEOGCS["WGS 84",DATUM["World > Geodetic System 1984", SPHEROID["WGS 84", 6378137.0, 298.257223563, > AUTHORITY["EPSG","7030"]],AUTHORITY["EPSG","6326"]],PRIMEM["Greenwich", 0.0, > AUTHORITY["EPSG","8901"]], UNIT["degree", 0.017453292519943295], > AXIS["Geodetic latitude", NORTH], AXIS["Geodetic longitude", EAST], > AUTHORITY["EPSG","4326"]], PROJECTION["Mercator (1SP)", > AUTHORITY["EPSG","9804"]], PARAMETER["semi_major", 6378137.0], > PARAMETER["semi_minor", 6378137.0], PARAMETER["latitude_of_origin", 0.0], > PARAMETER["central_meridian", 0.0], PARAMETER["scale_factor", 1.0], > PARAMETER["false_easting", 0.0], PARAMETER["false_northing", 0.0], UNIT["m", > 1.0], AXIS["Easting", EAST], AXIS["Northing", NORTH], > AUTHORITY["EPSG","900913"]]','+proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 > +lon_0=0.0 +x_0=0.0 +y_0=0 +k=1.0 +units=m +nadgri...@null +no_defs'); > > > *Get more information:* > * spherical_mercator.rst > * http://www.nabble.com/sphericalMercator-tf4625750.html#a13209474 > * > http://dev.openlayers.org/docs/files/OpenLayers/Layer/SphericalMercator-js.html > * http://trac.osgeo.org/gdal/ticket/1868: adding EPSG:900913 code to your > EPSG file. > > ---- > --- //[[yjaco...@free.fr|Yves Jacolin]] 2008/07/17 21:45// > _______________________________________________ > Dev mailing list > Dev@openlayers.org > http://openlayers.org/mailman/listinfo/dev -- Christopher Schmidt MetaCarta _______________________________________________ Dev mailing list Dev@openlayers.org http://openlayers.org/mailman/listinfo/dev
