Smathermather's Weblog

Remote Sensing, GIS, Ecology, and Oddball Techniques

GeoWebCache Configuration

Posted by smathermather on June 21, 2011

I’ve long delayed the configuration of GeoWebCache (GWC).  Automatic configuration within GeoServer’s deployment of it has been adequate until now.   Until now that I want to deploy tiles in something other than Google Mercator… .

I’ve developed a cache setup for Ohio State Plane North, Feet (epsg:3734).  At first it was a going to be a cache just for our service area, then I thought I’d include surrounding counties, and by the time I was done, I just decided that having a cache definition for the entire state plane ohio north coverage area made as much sense as anything else– it could make things easier to share and integrate as part of a regional standard for WMS-C, assuming I get buy-in from others… .  It could also be easily adapted for State Plane South.

The definition for a cache requires three things:  coordinate extent, resolutions (or equivalent), and tilesize (height and width).  For coordinate extent, I chose the extents of epsg:3734 as defined by spatialreference.org, and snapped them to the nearest 5000 foot interval:

1320000

160000

2525000

976000

Then, choosing resolution based on a series of measurable scales (1:600 or 1″=50′, 1:1200 or 1″=100′, etc) we get the resolutions:

918.6351706036746

229.65879265091866

58.20472440944883

45.931758530183735

29.102362204724415

22.047244094488192

14.220472440944883

11.023622047244096

8.818897637795276

8.267716535433072

5.511811023622048

4.409448818897638

2.204724409448819

1.1023622047244095

0.5511811023622047*

Finally, we’ll use a predictable tilesize:

<tileHeight>256</tileHeight>

<tileWidth>256</tileWidth>

Now we have a portable tilecache recommendation that should work for all of Northern Ohio:
GWC Example

3 Responses to “GeoWebCache Configuration”

  1. Paul said

    Hi,
    Maybe you could describe in more detail how resolutions were calculated? Formula or maybe detailed example?

  2. Kevin said

    Hi,
    Did you ever post these resolution calculations? I would be interested in those.

    Thanks

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

 
%d bloggers like this: