Implement Vector Tiling for SMAP

[linzjax]

Note: Not going into master

Proposed changes in this pull request

• implemented tile->lat/long converter
• view and template updated to serve vector tiles.
• added L.Deflate back (currently not working)
• added L.TileLayer.GeoJSON and updated to be compatible with Leaflet 1.0

When should this PR be merged

Whenever

Risks

None (Not going into master)

Follow up actions

• location.getBounds() currently not working because the geojsonTileLayer returned doesn't contain the spatial unit features.
• L.Deflate doesn't work with L.TileLayer.GeoJSON

Checklist (for reviewing)

General

• Is this PR explained thoroughly? All code changes must be accounted for in the PR description.
• Is the PR labeled correctly? It should have the migration label if a new migration is added.
• Is the risk level assessment sufficient? The risks section should contain all risks that might be introduced with the PR and which actions we need to take to mitigate these risks. Possible risks are database migrations, new libraries that need to be installed or changes to deployment scripts.

Functionality

• Are all requirements met? Compare implemented functionality with the requirements specification.
• Does the UI work as expected? There should be no Javascript errors in the console; all resources should load. There should be no unexpected errors. Deliberately try to break the feature to find out if there are corner cases that are not handled.

Code

• Do you fully understand the introduced changes to the code? If not ask for clarification, it might uncover ways to solve a problem in a more elegant and efficient way.
• Does the PR introduce any inefficient database requests? Use the debug server to check for duplicate requests.
• Are all necessary strings marked for translation? All strings that are exposed to users via the UI must be marked for translation.

Tests

• Are there sufficient test cases? Ensure that all components are tested individually; models, forms, and serializers should be tested in isolation even if a test for a view covers these components.
• If this is a bug fix, are tests for the issue in place There must be a test case for the bug to ensure the issue won’t regress. Make sure that the tests break without the new code to fix the issue.
• If this is a new feature or a significant change to an existing feature has the manual testing spreadsheet been updated with instructions for manual testing?

Documentation

• Are changes to the UI documented in the platform docs? If this PR introduces new platform site functionality or changes existing ones, the changes must be documented in the Cadasta Platform Documentation.
• Are changes to the API documented in the API docs? If this PR introduces new API functionality or changes existing ones, the changes must be documented in the API docs.
• Are reusable components documented? If this PR introduces components that are relevant to other developers (for instance a mixin for a view or a generic form) they should be documented in the Wiki.

[oliverroick]

The code looks good but there's one thing that bothers me (which is not your fault). The way L.TileLayer.GeoJSON is set up, it sends a lot of requests the the server which need to be processed. This makes sense when you provide different levels of geometry generalisation for each zoom level but not for our case. We want to load the geometry once and then don't worry about it any more when the map is zoomed or panned.

I thought about this a little and the best way to solve this is to keep track of the areas that have been downloaded already. I'm trying to come up with an idea to solve this efficiently. I'll keep you posted.