tile cache error : Lower left corner is outside layer bounds

Question

i have made a wms layers in openlayers consuming cached tiles generatred by tile cache , in the generation step i have used this configuration :

[vmap0] type=WMS url=http://localhost/cgi-bin/mapserv?map=maps/poimanager/nav 2tiles.map layers=nav_map bbox=-855822.40976158,3975513.7271299,-847686.6435646,3976531.2950689 levels=20

concerning the map in openlayers i have defined the resolutions in map instance options:

      var options = {
    maxExtent: new OpenLayers.Bounds(-2015494, 2445884, 48919, 4383204),
    projection: "EPSG:900913",
    displayProjection: new OpenLayers.Projection("EPSG:4326"),
    units: 'm',
    numZoomLevels: 20,
resolutions :[3.9725420883691527, 1.9862710441845763, 0.99313552209228817, 0.49656776104614408, 0.24828388052307204, 0.12414194026153602, 0.062070970130768011, 0.031035485065384005, 0.015517742532692003, 0.0077588712663460013, 0.0038794356331730007, 0.0019397178165865003, 0.00096985890829325017, 0.00048492945414662508, 0.00024246472707331254, 0.00012123236353665627, 6.0616181768328135e-05, 3.0308090884164068e-05, 1.5154045442082034e-05, 7.5770227210410169e-06]
            };

            var map = new OpenLayers.Map('map', options);

but i still get nothing just when i try to view the images using firebug it gimme this error :

"An error occurred: Lower left corner (-851825.191138, 3976933.501194) is outside layer bounds [-855822.40976158006, 3975513.7271298999, -847686.64356460003, 3976531.2950689001]. To remove this condition, set extent_type=loose in your configuration."

can you help me resolve this error :)

thanks in advance :)

Answer 1

Did you try what the error message suggested and set the extent_type to loose?

[vmap0]
type=WMS
url=http://localhost/cgi-bin/mapserv?map=maps/poimanager/nav 2tiles.map
layers=nav_map
bbox=-855822.40976158,3975513.7271299,-847686.6435646,3976531.2950689
levels=20
extent_type=loose

I've also had to update one of the Python files in TileCache to avoid the "too far from tile corner" errors on a couple of occasions using the patch outlined here.

If neither of these work then there is a problem with your bbox and the resolutions you have in OpenLayers. I'd set the maxExtent in OpenLayers to the extent of the world in EPSG:900913 and remove your resolutions parameter from your OpenLayers layer setup.

Answer 2

It is not enough to make the extents match. Setting the service bbox value and the OL map maxExtent to be the same value will not result in layers begin placed in the correct location. You must be very specific about the extent you choose. I've posted a tool here which provides an extent which corresponds to a tile in the web mercator projection.

For all of North America:

{"bottom":0,"left":-20037508.342784,"top":20037508.342784,"right":0}

For D.C. area:

{"bottom":4383204.949984,"left":-8766409.899968,"top":5009377.085696,"right":-8140237.7642560005}

Without using these extents I find that the TileCache WMS layers do not overlap with the same layer accessed directly (same WMS service without using TileCache).

An alternative may be possible to get this same result by providing tileOrigin, tileOriginCorner and tileSize when constructing the WMS layer. This approach will also require calculating the tileOrigin.

Answer 3

Hopefully it works :) just by setting srs to 900913

[vmap0] type=WMS url=http://localhost/cgi-bin/mapserv?map=maps/poimanager/navcities2tiles.map layers=navcities bbox=-2015494,2445884,48919,4383204 levels=20 extent_type=loose srs=EPSG:900913

thanks a lot geographika , your help is very interresting