We Visualize Your World

Exploring Options for Map Caching

Tile Cache Creation & ManagementPresented By:Jeremy Holt, GIS Consultant

02/17/2011

Whachutalkinbout?What we’ll cover with this session:

• An Overview

• Caching Explained (briefly)

• General Benefits of Map Caching

• Some Caching Terms and Concepts

• A Comparison of Available Tools

• Mapproxy, Tilecache, GeoWebCache, ArcGIS Server

• Functionality & Capabilities of Each

• Summary & Conclusion

• Choosing the Right Tool for the Job

• Consuming and Utilizing Cached Mapservices

Caching OverviewWell, what is map caching?

What types of things can I cache?

Got any Examples?

http://mt0.google.com/vt/lyrs=t@126,r@145&hl=en&x=2018&y=2949&z=13&s=Galhttp://mt0.google.com/vt/lyrs=t@126,r@145&hl=en&x=2018&y=2949&z=13&s=Gal

http://ecn.t2.tiles.virtualearth.net/tiles/r0213331100212?g=637&mkt=en-us&lbl=l1&stl=h&shading=hill&n=zhttp://ecn.t2.tiles.virtualearth.net/tiles/r0213331100212?g=637&mkt=en-us&lbl=l1&stl=h&shading=hill&n=z

http://services.arcgisonline.com/ArcGIS/rest/services/World_Topo_Map/MapServer/tile/13/2949/2018

http://services.arcgisonline.com/ArcGIS/rest/services/World_Topo_Map/MapServer/tile/13/2949/2018

Caching Overview

What are some benefits of having a cached mapservice?

•Lighten Browser load•Lighten Server load•Requests for small images rather than dynamic data rendering•Potential to improve performance

Caching Terms & Concepts

•Seeding

•Metatiling

•Tiling Schemes

•Image Types

•Transparency

•Projections / Reprojection

Caching Terms & Concepts

Seeding

Seeding is basically pre-rendering or dynamically creating map tiles based upon a defined extent or a geometry.

Seeding actions can be scripted, generated on-the-fly (user requests) or manually created.

Caching Terms & ConceptsMetatiling

A metatile consists of several tiles combined into one larger tile.

Pros:

Avoid duplicating the labeling of features that span more than one tile

Usually quicker for the WMS backend to generate one large image rather than many small ones

Cons:

Since the metatile is larger, it is slower to render than any individual tile

Memory consumption

Pros:

Avoid duplicating the labeling of features that span more than one tile

Usually quicker for the WMS backend to generate one large image rather than many small ones

Cons:

Since the metatile is larger, it is slower to render than any individual tile

Memory consumption

Caching Terms & Concepts

Tiling Schemes

Tiling schemes allow for definition of scale levels, tile size and sometimes coordinate system.

Setting tiling schemes for ArcGIS Server vary greatly than the other options we will review.

Caching Terms & Concepts

Image Types

Cached map tiles can be created/requested in different image formats. Most commonly .png for transparency and .jpeg for imagery.

Transparency

Transparency is used for overlaying tiles on top of other tiles and for sliding/transitioning effects. Supported with .png.

Also parameter in WMS request.

Projections / Reprojection

Most caches are created in a defined projection, but some utilities can reproject tiles (mapproxy).

How?

Consuming WMS and chopping it up into tiles

Stored in accessible directory to be returned to client

Application requests handled by cache utility

•Projection

•Location

•Tile size

•Image format

Comparison of Caching Utilities

MapProxy

MapProxy is an open source proxy for geospatial data. It caches, accelerates and transforms data from existing map services and serves any desktop or web GIS client.

MapProxy works like a simple tile cache, but also offers many new and innovative features like full support for WMS clients.

MapProxy is an open source technology used to create and serve up map caches. It is a middle-man between existing web map servers (like MapServer or GeoServer) and web map clients such as OpenLayers and GoogleEarth.

TileCache

TileCache is an implementation of a WMS-C compliant server made available under the BSD license by MetaCarta.

TileCache provides a Python-based WMS-C/TMS server, with pluggable caching mechanisms and rendering backends. In the simplest use case, TileCache requires only write access to a disk, the ability to run Python CGI scripts, and a WMS you want to be cached. With these resources, you can create your own local disk-based cache of any WMS server, and use the result in any WMS-C supporting client, like OpenLayers, or any TMS supporting client, like OpenLayers and worldKit.

GeoWebCache

“Maps are often static. As most mapping clients render WMS (Web Map Service) data every time they are queried, this can result in unnecessary processing and increased wait times. GeoWebCache optimizes this experience by saving (caching) map tiles as they are requested, in effect acting as a proxy between client (such as OpenLayers or Google Maps) and server (such as GeoServer, or any WMS-compliant server). As new maps and tiles are requested, GeoWebCache intercepts these calls and returns pre-rendered tiles if stored, or calls the server to render new tiles as necessary. Thus, once tiles are stored, the speed of map rendering increases many times, making for a more seamless user experience. GeoWebCache is one of the easiest ways to accelerate your WMS mapping server.”

A Matrix

So, ArcGIS Server already has Caching Tools…

Single mapservice focus

GUI / Geoprocessing options

Tailored for esri APIs

Compact Cache

Choose the Right Tool for the Job

All caching utilities are basically reading a mapservice, taking a snapshot of it and cutting it up into tiles defined by the user/tool. Once the tiles are created, they are stored in a directory structure similar to:

•Cache directory•Name of service•Scale levels•Row•Column•Image

This may change slightly based on what tool is doing the job, but typically tiles are sliced and stored around the grid-based system of level, row, column.

Utilizing Cached Services

Web Applications

ArcGIS Desktop

Geoportals/Opendata

Your Neighbor

Web Applications

ArcGIS Desktop

Geoportals/Opendata

Your Neighbor

ResourcesLinks!

http://mapproxy.org/

http://tilecache.org/

http://geowebcache.org/

http://help.arcgis.com/en/arcgisserver/10.0/help/arcgis_server_dotnet_help

/index.html#/What_is_map_caching/00930000006m000000/

Links!

http://mapproxy.org/

http://tilecache.org/

http://geowebcache.org/

http://help.arcgis.com/en/arcgisserver/10.0/help/arcgis_server_dotnet_help

/index.html#/What_is_map_caching/00930000006m000000/

Thanks!Feel free to ask any questions or share

your own tips.

1-715-874-4397

1-888-WeDoGIS

Jeremy.Holt@adc4gis.com