[OpenLayers-Users] wms query frustration

Fri Jun 6 08:28:17 EDT 2008

Have you set the correct tile size in openlayers?  The resolution it is
showing is double the max resolution.  This is probably because
openlayers is generating extents based on a particular tile size.  If
this size does not match what tilecache is using the resulting
resolution that tilecache calculates based on your extents will be
wrong.  Try explicitly setting the tile size in both openlayers and
tilecache to make sure.

Matthew

-----Original Message-----
From: users-bounces at openlayers.org [mailto:users-bounces at openlayers.org]
On Behalf Of Justin Palk
Sent: 05 June 2008 15:13
To: users at openlayers.org
Subject: [OpenLayers-Users] wms query frustration

Hi all -- I'm just starting out with openlayers, and I'm a little
frustrated.

I've been trying for a few days now to set up a simple map that will
let me query some hypothetical election results, but I keep running
into two snags:

1) When I first go to my test.html page, I'll get:
"An error occurred: can't find resolution index for 0.002231.
Available resolutions are: [0.0011154260000000001,
0.00055771300000000005, 0.00027885650000000002, 0.00013942825000000001
(etc.)"

I can't figure out why I'm starting at a resolution of 0.002231 when I
set a maxResolution of 0.001115426.

2) If I zoom in one step (to resolution 0.001115426) I get the following
error:
"An error occurred: Current x value -77.535047 is too far from tile
corner x -77.677821"
The "Current x value" never seems to change regardless of where I
click on the map.

I can only assume this is some sort of projection error, but I've been
beating my head against the wall checking and double-checking my srs's
and resolutions, but I can't seem to find a solution. Any suggestions
would be greatly appreciated.

I'm working with a map in EPSG:4326
ogrinfo -so returns:
INFO: Open of `election_4326.shp'
      using driver `ESRI Shapefile' successful.

Layer name: election_4326
Geometry: Polygon
Feature Count: 61
Extent: (-77.677821, 39.219771) - (-77.106723, 39.719845)
Layer SRS WKT:
GEOGCS["GCS_WGS_1984",
    DATUM["WGS_1984",
        SPHEROID["WGS_1984",6378137,298.257223563]],
    PRIMEM["Greenwich",0],
    UNIT["Degree",0.017453292519943295]]
ED_NUM: Integer (10.0)
ED_NAME: String (16.0)
PRECINCT: String (6.0)
LEGIS_DIST: String (3.0)
POLL_NAME: String (50.0)
POLL_TYPE: String (40.0)
POLL_ADDRE: String (40.0)
CITY: String (25.0)
ZIP_CODE: String (15.0)
SHAPE_area: Real (19.11)
SHAPE_len: Real (19.11)

Here's the relevant bit from my tilecache.cfg:
[election_results]
type=MapnikLayer
mapfile=/tmp/ed.xml
extent_type=loose
bbox=-77.677821,39.219771,-77.106723,39.719845
maxResolution = 0.001115426

The map line from ed.xml:
<Map bgcolor="steelblue" srs="+proj=longlat +ellps=WGS84 +datum=WGS84
+no_defs">

and my script:

	<script type="text/javascript">
			OpenLayers.ProxyHost =
"/cgi-bin/proxy.cgi?url=";
			var map = new OpenLayers.Map("map",
			{maxExtent: new
OpenLayers.Bounds(-77.677821,39.219771,-77.106723,39.719845),
			maxResolution:0.001115426}
			);

			var er = new
OpenLayers.Layer.WMS("election_results",

"http://127.0.0.1/cgi-bin/tilecache-2.03/tilecache.cgi?",
{layers: 'election_results', format: 'image/png', projection:
"EPSG:4326"});

			map.addLayer(er);

			map.addControl(new
OpenLayers.Control.Permalink());

			map.zoomToMaxExtent();

			map.events.register('click', map, function (e){

OpenLayers.Util.getElement('nodeList').innerHTML = "Loading...";
					var url =
er.getFullRequestString({
						REQUEST:
"GetFeatureInfo",
						EXCEPTIONS:
"application/vnd.ogc.se_xml",
						BBOX:
er.map.getExtent().toBBOX(),
						X: e.xy.x,
						Y: e.xy.y,
						INFO_FORMAT:
'text/html',
						OUERY_LAYERS:
er.params.LAYERS,
						WIDTH: er.map.size.w,
						HEIGHT: er.map.size.h});
					OpenLayers.loadURL(url, '',
this, setHTML);
					OpenLayers.Event.stop(e);
				}
				);

				function setHTML(response){

OpenLayers.Util.getElement('nodeList').innerHTML =
response.responseText;
					}

		</script>

-- 
"News is what people want to keep hidden, and everything else is
publicity"
 --Bill Moyers
_______________________________________________
Users mailing list
Users at openlayers.org
http://openlayers.org/mailman/listinfo/users
This e-mail message and any attached file is the property of the sender and is sent in confidence to the addressee only. The contents are not to be disclosed to anyone other than
the addressee. Unauthorised recipients are requested to preserve this confidentiality and to advise the sender immediately of any error in transmission. If you experience difficulty 
with opening any attachments to this message, or with sending a reply by email, please telephone on + 44-(0)1235 438151 or fax on + 44-(0)1235 438188. 
Any advice contained in this e-mail or any accompanying file attached hereto is for information purposes only. RPS do not take any responsibility for differences between the original 
and the transmission copy or any amendments made thereafter. If the addressee requires RPS to be responsible for the contents of this e-mail, RPS will be pleased to issue a signed 
hard copy of the document upon request.
RPS Group Plc, company number: 208 7786 (England). Registered office: Centurion Court, 85 Milton Park Abingdon Oxfordshire OX14 4RY.
RPS Group Plc web link: <http://www.rpsgroup.com>