OpenLayers 3 + POST + RequireJS

Adds the option of sending tile requests using POST (as well as still using GET).

Fixes a conflict with RequireJS that makes loading ol-debug.js fail because of rbush.

Warning

This project is still not complete. I'm pushing too soon.

(The AMD/rbush fix does work, but currently the POST feature is still a baby.)

Features/Musings

Why POST?

Because a project's request URL might otherwise be greater than the lowest common denominator 2,083 character limit imposed by IE8.

Although, even if the request limit might be the next LCD, which is 65,536, not all servers accept large GET request strings. See boutell's urllength for a list of clients and servers and their url limits.

Also, POST requests can be unlimited, so having an a priori mandate seems unreasonable, especially considering that there's no way of knowing what kind of request data might need to be sent from client to server (e.g., spatial queries, Don Quixote, etc.).

Alternatives to POST

The client could POST the tile query data before issuing the tile GET request. The server would have to cache the request and return a token to the client to use in the next (and possibly subsequent) tile request(s).

• This solution seems unnecessarily complicated, especially since OpenLayers already caches requests. You don't get any performance gain; you get bragging rights to a more complicated implementation.

What's Wrong with OpenLayers and RequireJS and rbush?

If a project uses RequireJs to load OpenLayer 3, loading ol-debug.js fails on Uncaught TypeError: ol.ext.rbush is not a function.

The production build, ol.js, works fine.

The problem is that the external rbush library checks on the define.amd object and attribute and sees that it's set, so it exports itself amd-style. But goog.require expects it to be exported goog-style.

The reason the release build works is because the reference to define.amd is mangled in the release build, e.g., it looks like define.Mo, so the rbush module is then exported goog-style.

• See the modified rbush module and the modified lines.

Note

FIXME: The author needs to open a ticket with rbush. If they accept that patch, the npm registry will be updated, and then the stock OpenLayers project will work. But I'm busy on a work deadline and can't wait, so I've just cloned those projects and moved along.

Also, fixing rbush for an AMD-project-that-imports-a-Closure-project-that-imports-rbush will probably break rbush for the reverse, that is, a Closure-project-that-imports-an-AMD-project-that-imports-rbush might break if the rbush team accepts this patch. Ideally, the rbush code -- since it's part of an import progression, or whatever it's called -- should let the caller tell it how to export itself.

The OL3/AMD/rbush issue is being tracked in OpenLayers as requirejs optimization issue with ol3 (#3274).

Unresolved Issues

The debug build is sometimes known to not draw ol.source.Vector linestrings, and those layers, albeit transparent when drawn, can obscure other layers, such as label layers created with ol.layer.Image. At least in this author's experience.

Compiling on Debian/Ubuntu/Linux Mint

The OL3 compilation instructions omit problems encountered in Debian distros.

Hence these instructions.

Note

These instructions have only been tested on Linux Mint 17.1. But the author guesses they'll work in Ubuntu, tuu.

Note

On Ubuntu 12.04 LTS in a chroot, the npm install command fails while trying to download files. The author is not aware if this is a chroot problem or an old-distro problem.

Install build tools

sudo apt-get install default-jdk
sudo apt-get install default-jre
sudo apt-get install nodejs
sudo apt-get install npm

Debian renames the node executable, but the OL3 code doesn't know that. So fake it.

sudo /bin/ln -s /usr/bin/nodejs /usr/bin/node

Here's the quickest way to build the OL3 library.

# cd some/where
npm install landonb/ol3
cd ol3/node_modules/openlayers
sudo pip2 install -r requirements.txt

You can alternatively use easy_install: cat requirements.txt | sudo xargs easy_install but most sane people no longer use easy_install.

You can also clone the repository manually or extract it from an archive, in which case instead of npm install landonb/ol3 you'll simply run npm install after cloning or unpacking. (And try make check-deps if you want to check that java, node, and npm are installed.)

Build the code

Note

On the first build, npm will download all of the remote dependencies. So the first build always takes longer.

This is easy.

make build

And that's it.

If you want to create smaller binaries, create an ol.json file and specify exactly which features (classes and functions) you'd like packaged.

• See Creating custom builds

Other make commands include:

• make clean - run this if you edit third-party code and want to re-build.
• make server - run this is you want a simple server to test your code against.
• make lint - run this to check your code, especially important if you want to contribute to OpenLayers development.
• make test - run this if you plan to contribute patches.
• make check - always run this before asking OL3 devs to pull your code.