[OpenLayers-Users] new user questions
Greg Donald
gdonald at gmail.com
Sat Oct 4 14:48:14 EDT 2008
I've been learning the Openlayers API for several days now and have
some questions I can't seem to find answers for in the mailing list
archives.
1) How can I construct bounds that only have positive numbers? When I
try this bit of code I still get negative numbers in my tile requests:
maxExtent: new OpenLayers.Bounds( 0, 0, 300000, 7000000 )
Is it possible to make a grid that works top-down, left to right, 0 up
to whatever, both horizontally and vertically?
0 1 2 3
1
2
3
2) I want to create 5 different depths of data display. Do I need to
construct 5 individual layers or is one layer sufficient since I plan
to request tiles based on coordinates? I don't see any sort of
"layer" variable arriving in my tile request variables.
layer = new OpenLayers.Layer.MapServer( "Level 1", "/image/", {}, {} );
http://dev.openlayers.org/releases/OpenLayers-2.6/doc/apidocs/files/OpenLayers/Layer/MapServer-js.html
I've read the above URL, but where can I find api documentation for
the last two constructor parameters? Is this possibly where I would
define the "layer" I'm requesting as far the tile requests?
3) Where can I find documenation for these tile request variables?
{"imgy"=>"128", "map_imagetype"=>"png", "imgext"=>"-1680 1000 -1320
1360", "mode"=>"map", "imgxy"=>"256 256", "map_size"=>"256 256",
"mapext"=>"-1680 1000 -1320 1360", "imgx"=>"128"}
Looking at the "imgext" request variable, is -1680,1000 the bottom
left and -1320,1360 the top right? How does this corelate to a
256x256 tile size?
What's the difference between "imgext" and "mapext"? They always seem
to be the same.
Why isn't map_size "300000 7000000" like I defined it above?
Here's my code so far:
<script type="text/javascript">
var lon = 0;
var lat = 0;
var zoom = 1;
var map, layer;
function init()
{
var options = {
numZoomLevels: 1,
maxExtent: new OpenLayers.Bounds( 0, 0, 300000, 7000000 ),
};
map = new OpenLayers.Map( 'map', options );
layer = new OpenLayers.Layer.MapServer( "Level 1", "/image/", {} );
map.addLayer( layer );
map.setCenter( new OpenLayers.LonLat( lon, lat ), zoom );
map.removeControl( map.controls[ 1 ] );
map.addControl( new OpenLayers.Control.LayerSwitcher() );
map.addControl( new OpenLayers.Control.PanZoomBar() );
map.addControl( new OpenLayers.Control.MousePosition() );
map.addControl( new OpenLayers.Control.OverviewMap() );
map.addControl( new OpenLayers.Control.KeyboardDefaults() );
}
</script>
<div id="map"></div>
Thanks,
--
Greg Donald
http://destiney.com/
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