[OpenLayers-Users] OpenLayers Optimizing page load time (reducing size of polygons) and preventing IDL polyong splits.

[brad]

Coop,

 

When you load data to the client you run into these problems. I assume you
need to load these into the client to give better responsiveness at the
client for things like mouseover? 

 

Anyway, I know its application dependent but I prefer to leave everything on
the server and when you need access to the geometry/attributes in realtime
you undertake a WFS GetFeature request. You should also transfer the data in
compressed form - eg binary XML - to keep the download time to a minimum.
This is a trade off in responsiveness but you retain all the geometry that's
in your database all the time and your WFS request can include a different
SRS so all transformations are done at the server level for the requested
area - Area Of Interest - only. You can also use WMS GetFeatureInfo to get
the attributes only for any picked polygon. You can also use SLDs to render
thematic maps on the server which takes away a lot of client code if you are
doing that as well at the client with these polygons.

 

Maybe not what you wanted to hear but there is no free lunch in this regard.

 

Cheers,

 

 

Brad Spencer

Managing Director,  NuMaps

http://www.numaps.com.au/

tel: 02 9672 6856

mob: 0404 841 131

 

 

From: openlayers-users-bounces at lists.osgeo.org
[mailto:openlayers-users-bounces at lists.osgeo.org] On Behalf Of Coup Coup
Sent: Tuesday, 26 April 2011 5:22 AM
To: openlayers-users at lists.osgeo.org
Subject: [OpenLayers-Users] OpenLayers Optimizing page load time (reducing
size of polygons) and preventing IDL polyong splits.

 

Hello,
I have built a (using django postgis and openlayers) display about 200
specific polygon shapes consisting of clusters of counties in the US
(including Alaska, Puerto Rico and Hawaii). I am displaying using Google as
base map and then applying the polygons to features which I attach to one of
10 layers. I am transforming the data to projection 900913 and displaying
the features as vectors.

I have two issues I am looking for feedback or suggestions on:
1. Map load optimization:
The data is almost 1MB. I have applied the simplify utility and whittled
down the number of points in each polygon (which was as high as 8,000) down
to an average of 150 per shape. (Some polygons cant be simplfied or they
will lose their entire shape). I tried to unionagg() the entire list of
polygons into 1 but I lose so much definition and will also lose the ability
to enhance the map by allowing individual selection and labelling. Is there
a way to get the data set even smaller without losing shape quality?

2. One of the polygons is in Alaska, and encompasses the islands in the
Aleutians West. Upon completion of the building the map, I'm calling
map.zoomToExtent(bounds); (where bounds is the collective bounds of all of
the polygons) and because Aleutians West is so close in proximity to the IDL
(international date line) it is placing part of the polygon on either side
of the map so it is zooming way out (so you can see the whole world map) and
splitting repeating the polygon on the respective portion of the map. Is
there a way to move the IDL so it wont try to split it in this way?


Thanks for any knowledge you can share.

Coop

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