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Common pitfalls for users of OpenLayers by Marc Jansen of Terestris
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2011-09-14 | FOSS4G 2011 | M. Jansen: „Common OpenLayers pitfalls“ 1
FOSS4G 2011, Denver, CO
Common pitfalls for users of OpenLayers
Or: “Why are my features at the equator
when they shouldn't“
Marc Jansen, terrestris GmbH & Co. KG
2011-09-14 | FOSS4G 2011 | M. Jansen: „Common OpenLayers pitfalls“ 2
Table of contents
● Introduction● Methodology● Common pitfalls● Homework
or how to improveOpenLayers
[pitfall]
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Introduction – about me
● Marc Jansen● Developer and project manager
@ terrestris● Frontend and
OpenSource-GIS-Stack● Co-Author „OpenLayers —
Webentwicklung mit dynami-schen Karten und Geodaten“ (ISBN 978-3-937514-92-5)
● Trunk committer OpenLayers
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Introduction – about terrestris
● OpenSource WebGIS Technologies● Softwaredevelopment● Training & Consulting● OpenSource advocates
● Geoportals, Geodata, Standards...● Partner of OpenGeo● Sponsoring FOSS4G, FOSSGIS● Associate member of OGC
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Introduction – this talk
● This talk will deal with OpenLayers...
● … a quick poll
2011-09-14 | FOSS4G 2011 | M. Jansen: „Common OpenLayers pitfalls“ 6
Raise your hands, please
Who knows OpenLayers
?
2011-09-14 | FOSS4G 2011 | M. Jansen: „Common OpenLayers pitfalls“ 7
Raise your hands, please
Who has developedusing OpenLayers
?
2011-09-14 | FOSS4G 2011 | M. Jansen: „Common OpenLayers pitfalls“ 8
Raise your hands, please
Who knows theonline API-documentation
?
2011-09-14 | FOSS4G 2011 | M. Jansen: „Common OpenLayers pitfalls“ 9
Raise your hands, please
Who thinks theonline API-documentation
totally rocks
?
2011-09-14 | FOSS4G 2011 | M. Jansen: „Common OpenLayers pitfalls“ 10
Raise your hands, please
2011-09-14 | FOSS4G 2011 | M. Jansen: „Common OpenLayers pitfalls“ 11
Methodology
● This is not a scientific talk● Sources:
● OpenLayers-User List [userlist]
● Stack Overflow [stackoverflow]
● Twitter [twitter]
● My experience
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Vectors
● Many problems circle around vectors in OpenLayers● Styling● Performance● Custom Select-Tools● Get Features from services● use cases range from easy to complex
2011-09-14 | FOSS4G 2011 | M. Jansen: „Common OpenLayers pitfalls“ 13
Styling Vectors
● You can set● style for a feature● style for a layer● stylemap for a layer
– render intents– attributive '${statusClass}'– rule based
● Complex styling options
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Performance of Vectors
● Internet Explorerhas big issues renderingmany (> 250) features~
● Usual suggestion● Raster layer for display● Limit features● Cluster strategies● Drop support for IE
(often not an option)
[ie-logo]
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Performance of Vectors
2011-09-14 | FOSS4G 2011 | M. Jansen: „Common OpenLayers pitfalls“ 16
Custom Select-Tools for Vectors
● Select by a box● { box: true }
● Select by a polygon● { poly: true }● (currently not available!)
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Getting Features from a service
var kml = new OpenLayers.Layer.Vector("KML", { strategies: [ new OpenLayers.Strategy.Fixed() ], protocol: new OpenLayers.Protocol.HTTP({ url: "kml/sundials.kml", format: new OpenLayers.Format.KML({ extractStyles: true, extractAttributes: true }) }) });
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Projections
● Projections in OpenLayers● Reprojection of data● WMS in different projection
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Known Projections
● Projections in OpenLayers● 4326 and 900913
new OpenLayers.Map( { projection : 'EPSG:31467', maxResolution: 30000, units: 'm', maxExtent: new OpenLayers.Bounds( 3146150, 5223600, 4031150, 6108600 )} );
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OpenLayers with another SRS
[ger
man
y-w
ms]
2011-09-14 | FOSS4G 2011 | M. Jansen: „Common OpenLayers pitfalls“ 21
● Included: 4326 <=> 900913● Otherwise: Proj4 JS http://proj4js.org/
Reprojection of vectordata
<script type=“text/javascript“ src=“path/to/proj4.js“></script><script type=“text/javascript“> Proj4js.defs["EPSG:31467"] = "+proj=tmerc +lat_0=0 +lon_0=9 +k=1 …";</script><script type=“text/javascript“> var geom = new OpenLayers.Geometry.Point(6.97, 50.95); geom.transform( new OpenLayers.Projection('EPSG:4326'), new OpenLayers.Projection('EPSG:31467') );</script>
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Reprojection of vectordata
[ger
man
y-w
ms]
2011-09-14 | FOSS4G 2011 | M. Jansen: „Common OpenLayers pitfalls“ 23
Projections
● My SRS URL-parameter is being ignored!● That's because
● The baselayer determines the projection that will end up in the URL
● or● The OpenLayers.Map-instance has a projection.
2011-09-14 | FOSS4G 2011 | M. Jansen: „Common OpenLayers pitfalls“ 24
API
● Too complex for simple things● Popup, marker, tooltips, annotations● Compare to Leaflet (http://leaflet.cloudmade.com/)● http://crschmidt.net/blog/archives/497/demo-leafletopenlayers-translator/
● Silent failures● Debug mode● Swapping of base library
2011-09-14 | FOSS4G 2011 | M. Jansen: „Common OpenLayers pitfalls“ 25
Documentation
● … or lack of documentation● … or in too many different places
● e.g. Vector styling
● Outdated examples● No inherited properties in API● Events / callback / arguments
2011-09-14 | FOSS4G 2011 | M. Jansen: „Common OpenLayers pitfalls“ 26
Performance
● Vectors (see before)● Single file build / compressing
● build/build.py and build/README.txt● http://openlayerer.appspot.com/
● WMS tiling● Web Best practices
(gzip, cssmin, header etc)
2011-09-14 | FOSS4G 2011 | M. Jansen: „Common OpenLayers pitfalls“ 27
What wasn't a problem?
● There were (surprisingly) very few questions related to● Same Origin Policy and proxy.cgi● Mobile● Browser X does Y instead of Z
2011-09-14 | FOSS4G 2011 | M. Jansen: „Common OpenLayers pitfalls“ 28
Homework
● For OpenLayers● Better documentation (=> Codesprint Fr?)● Better API
● For you● Tell us what is annoying● Send patches / edit on github● Get involved!
2011-09-14 | FOSS4G 2011 | M. Jansen: „Common OpenLayers pitfalls“ 29
Thanks
Thank youfor your attention.
Questions?
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Sources● [userlist]: http://lists.osgeo.org/pipermail/openlayers-users/
● [stackoverflow]: http://stackoverflow.com/questions/tagged/openlayers
● [twitter]: http://twitter.com/#!/selectoid/status/99382702867877888
● [ie-logo]: http://paulirish.com/2010/high-res-browser-icons/
● [germany-wms]: http://wms1.ccgis.de/cgi-bin/mapserv?MAP=/data/umn/germany/germany.map&REQUEST=GetCapabilities&SERVICE=WMS&VERSION=1.1.1
● [pitfall]: http://www.flickr.com/photos/montage_man/394251850/ CC-BY 2.0 by joefoodie
2011-09-14 | FOSS4G 2011 | M. Jansen: „Common OpenLayers pitfalls“ 31
Imprint
● Author:Marc Jansen @selectoidterrestris GmbH & Co. KG http://terrestris.de/Irmintrudisstr. 17 [email protected] Bonn, GermanyTel. +49 228 – 962 899 53 Fax: +49 228 – 962 899 57
● Licence of the slides:Creative Commons (by-sa) 2.0-Licencehttp://creativecommons.org/licenses/by-sa/2.0/
