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Mapnik based tile map server

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README.markdown

nanomaps-server

This is a simple tile map server written in Java. It uses Netty to implement the HTTP server and should therefore be moderately memory efficient when it comes to serving a large number of clients. Also, since it runs in a single process, it opens the door for some better traffic control mechanisms than are (easily) possible with other solutions that run within apache or other http servers.

It internally uses Mapnik to render the maps via the Mapnik JNI bindings.

It also leverages SQLite via some hacked custom Java bindings that are based on sqlite4java to manage tile caching. This part is still being worked on offline and is not in this repo.

Everything is self contained in this repo. You don't need any Java expertise to use it.

Why

Because I'm a Java programmer and I needed something to serve my Mapnik xml files. I found it easier to just mock something up quickly in Java than going to the store and buying a bottle of Advil to combat the headache that would ensue if I tried to remember all of the stuff that I used to know about deploying Apache modules, python wsgi stuff, et al. I realize that most people feel that way when coming to Java, but c'est la vie. We all have our habits. I had the basic skeleton of what I needed from other projects so it wasn't that hard.

I was thinking it would just be a little development toy, but it kind of grew on me. I like that I can just clone the git repo on my server, run a couple of commands and start rendering maps.

Quick Start

Prerequisites

You need to have Mapnik2 (aka SVN trunk) checked out and built to a standard location (I have only tested with installs to /usr/local). There are multiple sources out there telling you how to do this. If you have the following paths on your box, you are probably in good shape:

  • /usr/local/lib/libmapnik2.so (or .dylib if on osx)
  • /usr/local/lib/mapnik2/input/
  • /usr/local/lib/mapnik2/fonts/

This is probably also the right time to let you know that you are going to need a Java 6 JDK and Apache Ant >= 1.7. This is the part where if you're not a Java person, you break off the date and go home and complain to your friends. But do not fear, this paragraph represents the sum total of what you need to know about Java in order to proceed. If you are running any non ancient version of OSX, you're probably set out of the box. If you are on Ubuntu, the following packages should get you going (trimming this down for servers and headless machines is left as an exercise to the reader):

  • apt-get install openjdk-6-jdk
  • apt-get install ant

If you are on Windows, you have my condolences.

Clone Repository

git clone --recursive git://github.com/SpatialInteractive/nanomaps-server.git
cd nanomaps-server

# Skip the following if you cloned recursively
scripts/update-modules.sh

Build dependencies

ant depend

This is the part where if something can go wrong it will. Everything in the external/directory is built, including native bits. If your build environment has issues, you will get errors on the native build steps. If you managed to build mapnik and its input plugins, you should be fine.

Run the server at the console

ant instance
ant run

(Note that if you're living dangerously, you can just execute 'ant run' right after checkout. This will take care of everything for you but if something goes wrong, it's going to be a little difficult to figure out what happened)

Load it up in your browser

http://localhost:7666/

You should get a web page with the colorized population map as presented here. At the top left is a drop down of maps that were found in the instance/repository directory when the server started. The default install only has the one "world_sample" but if you drop other *.mapnik.xml files into the repository directory (and restart), they should show up here. The ui is Nanomaps JS and should work on modern desktop browsers and mobile.

Screenshots

Default Installation

First Screen

Zoomed In on a MapQuest OSM Map

This is a proof of life of the server rendering a non-trivial OSM map. The source is actually a highly optimized fork of the (MapQuest OSM Style)[https://github.com/MapQuest/MapQuest-Mapnik-Style] rendered off of SQLite databases that have been optimized with another tool I've been working on called Mapnik Distiller.
It applies a number of optimizations to the OSM database with the end result being that functional, relatively high performance maps can be rendered on modest hardware. I've been running it on a 6 year old Linux desktop with 2GB of RAM with pretty decent rendering performance at all zoom levels (~250ms/tile depending on zoom level).

MapQuest OSM

Configuration

Server configuration is currently hard-coded or auto detected. I'll be adding bits to make it all configurable shortly. The primary moving part is the files that you put in the instance/repository directory.

The server will pick up files with the following name patterns and publish them:

  • {mapname}.mapnik.xml
  • {mapname}.select.js

In addition, some properties control the way that the maps are exposed. These will be read from {mapname}.properties if it exists. Currently, the following properties are supported:

  • announce: If "false" then the map will not be listed in the server's table of contents
  • attribution: Text attribution listed with the map metadata
  • attributionHtml: Html attribution listed with the map metadata

Everyone here should already know what goes into a *.mapnik.xml file, so I won't go into that except to make one note: If you use a symlink, then the server resolves the link and passes the resolved path to mapnik for loading. The result is that if your symlinked map file references relative resources, those resources will be resolved relative to the actual endpoint of the link, not the link itself.

Also, the server makes aggressive use of etags for http caching. The etag is calculated off of the "completely loaded" contents of the repository file (ie. the mapnik.xml or the select.js file). Therefore, if the file contents haven't changed, all generated maps will have the same etag. Note that entities are resolved in mapnik.xml files prior to calculating the etag.

JavaScript Map Select Files

The server is organized to support a number of pseudo map types that are identified by file type in the repository directory. Eventually, I expect to have proxy types and other constructions useful for stitching multiple maps together. Right now, there is just the .select.js file which is a little chunk of JavaScript that takes a map request and decides what underlying map should be rendered. I needed this straight away because my OSM maps are broken into four different detail levels and something needs to pick the right one to render for each request.

Here is an example:

function select(request) {
    var level=request.level, suffix;
    if (level>=15) suffix="dl1";
    else if (level>=11) suffix="dl2";
    else if (level>=7) suffix="dl3";
    else if (level>=1) suffix="dl4";

    if (suffix) {
        logger.info("Select detail level " + suffix + " for level " + level);
        return "mqstreet_" + suffix;
    } else {
        return null;
    }
}

Currently, there are two global objects available:

  • repository: The object that manages the repository. Can be used to lookup additional things.
  • logger: A SLF4J logger

The js file should define a function "select" that takes a request parameter and returns something that can be turned into a map such as:

  • A map name. The invoker will recursively resolve any returned string against the repository to produce a map. Cyclic recursion is detected and stopped.
  • A MapLocator object. You can get one of these from repository.lookupMap(name). Or conceivably, you could instantiate some special kind of MapLocator and give it back
  • A MapResource object. This is the type of object that actually gets rendered. There is presently not a straight-forward way to create one of these from the JavaScript side.

The request object given to the select() method has the following properties:

  • tileWidth
  • tileHeight
  • mapName
  • level
  • x
  • y
  • cost
  • time

It is highly likely that I will refactor this class before too much longer, so I'm not going to document these properties further.

Something went wrong with that request. Please try again.