But Apple's geospatial support is still... mediocre, particular given what they must be paying for the map. I got to thinking: What would make geospatial display work better on iOS and OS/X?
First, what am I talking about?
Geospatial data display is maps and globes. A weather app is a geospatial app, as is any sort of map app and so is an Atlas.
|Globe, map. Map, globe. Same thing.|
Geospatial is what I do. I make a popular toolkit for map and globe data display on iOS (and <cough> Android </cough>). Presenting geospatial display to developers in a way they can handle is what I do.
And that leads to the important question: What's wrong with the way Apple does it now?
The Current Situation on iOS (and OS/X)
Let's use weather as an example. Everyone loves (or hates) their weather app. In any case, they have an opinion. So how do you make a serious weather app, with animated radar and such?
You build a serious weather app in one of two ways: Core Graphics or OpenGL ES. You can tell which was used immediately. Is it a little weird and janky (Core Graphics) or smooth and pretty (OpenGL)?
Why that is has a little to do with rendering and a lot to do with data management. The way you display 20 pins in UIViews is not the way you render 20 layers of animated streaming radar data.
And okay, that's a hard case, but it's also plain old map apps that are kind of 'meh' under Core Graphics. There's another reason for that.
MapKit Under Glass
The Maps App is a big, capable and (I imagine) very expensive system. It does a lot and it's pretty good at it. MapKit looks to be a sort of wrapper on top of it. That's a problem.
|Hands up. Who's reimplemented that compass?|
You can't change the bulk of what MapKit is displaying. Sure, you've got a few knobs to twiddle and you can toss a little of your data on top, but only grudgingly. But there's an even bigger issue. MapKit was obviously (obviously!) written with OpenGL ES, but none of that infrastructure is available to the rest of us.
So here's the question. If you scooped out MapKit's brains and made neat little piles, what would that (unfortunate metaphor) look like?
I think you'd start with CATiledLayer, the go-to data structure for the pre-OpenGL map era. As a reminder, CATiledLayer will break the world into little pieces and tell you when to load those pieces.
|Something like this|
A new CATiledLayer is a good place to start, but it's probably a bit low level and it's missing one giant thing: A Spatial Reference System.
Adding an SRS to a CATiledLayer(-like thing) would solve the first set of problems. Your data could exist in one system while displaying in another. I'd also make the levels and loading strategies explicit with budgets for tiles and such. And threads everywhere. EVERYWHERE.
|One tile loading strategy|
That helps with loading, but what do you do once you've got that little image or basket of vectors for a tile. How do you render it fast?
With Core Graphics, you really don't render it fast. And the layer based image solutions are kind of weak. It's time to drill a hole in UIKit and plunge into the icy waters of OpenGL ES.
Images, Vectors, and Shaders - Oh My!
Most of what you want to display on a map is pretty simple: Image tiles, symbols, text, lines, and polygons. All pretty easy to display slow, but hard to render fast.
|Sometimes a map is just a map|
Here's what you do. You develop a little system for abstracting those object types to hand to a renderer. Then let the system manage them, batch them and move them around. Essentially you've moved the developers job off into other threads: Just load the data and let the system handle it.
This is suspiciously similar to what I do in WhirlyGlobe-Maply.
What About The Globe?
Well, yes, everyone loves the globe; even developers who should know better. User interaction with a globe is just different from a map and switching between the two makes life harder than it needs to be (looking at you MapKit).
|Globe + Weather = Awesome|
But the globe is cool, so where do you put it? SceneKit. SceneKit is where you put it.
Pull the tile loading logic from CATiledLayer++ above, make a nice globe surface and voila! You can reuse most of what you build for the 2D maps. Sure, it's a little more work to set up SceneKit and live in OpenGL-land. But globe.
Aaaaand back to MapKit
Okay, so you've built up a nice rendering infrastructure for map tiles, vectors, symbols and other such stuff. It gets along with both UIViews and SceneKit. But does it use anything from MapKit? It also begs the question: Should you rewrite MapKit in this stuff?
No. Good grief, no. Only interns and the criminally insane rewrite working systems for the hell of it. Instead, you steal data from the map.
|Nothing personal, Santa Rosa|
Apple Maps has a number of interesting data layers it would be fantastic to reuse in other apps: Roads, water, symbols, land, parks, and labels to name a few. Especially labels, which would make one of my dreams come true: Putting the @%&#@ labels on top of the animated radar.
Map Data Reuse
Mere mortals can't reuse Apple Maps data... but Apple could. If they started teasing it apart and tossing it into a system like I've described above, it would make maps apps that much more interesting. And yes, the label thing, which bugs me a lot. Seriously, that's annoying.
This would also let us mix and match data from varying sources. There are some excellent map tiles out there and I'm sure Apple could come up with a few more of its own that don't quite belong in what they've got now.
Wrapping it Up
I've skipped over a few details, but here's the basic story.
- Add a Spatial Reference System for selected layers
- Soup up CATiledLayer for some serious tile management
- Drill a hole down to OpenGL ES (and/or Metal) for some decent primitive display.
- Globe meet SceneKit. SceneKit, globe.
- Start pulling data layers out of the map source.
Do that, Apple, and you've got yourself some seriously reusable geospatial display support. It would be interesting to see what came of it.