Posted on December 27, 2022 (Updated on July 21, 2025)

Leaflet CRS.Simple or CRS.EPSG3857 conversion Problem

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Leaflet Coordinate Systems: Untangling CRS.Simple and EPSG:3857

So, you’re diving into Leaflet, the awesome JavaScript library for whipping up interactive maps? Fantastic! But sooner or later, you’re going to bump into Coordinate Reference Systems (CRSs). Trust me, understanding these things is key, especially when you’re venturing beyond standard map scenarios. CRS.Simple and CRS.EPSG3857? They’re often the culprits behind head-scratching moments. Let’s break it down, shall we?

CRSs: The Foundation of Map Accuracy

Think of a CRS as the blueprint for your map. It’s how we take the Earth’s curved surface and flatten it onto your screen. It’s what ensures that when you plot a point, it lands where it’s supposed to. Leaflet uses CRSs to translate those geographical coordinates into the pixel-perfect spots you see on your map. Get the CRS wrong, and… well, let’s just say things get messy fast.

EPSG:3857: The King of Web Maps

CRS.EPSG3857 – also known as Web Mercator – is basically the web mapping world’s MVP. It’s Leaflet’s default, and almost every tile provider out there (think Google Maps, OpenStreetMap) uses it. Why? It’s relatively simple to calculate, which makes things speedy. The catch? It distorts things, especially the further you get from the equator. Greenland looks HUGE, right? That’s EPSG:3857 at work. It measures things in meters.

CRS.Simple: Your Blank Canvas

Now, CRS.Simple is where things get interesting. Forget about geography for a second. Think of it as a plain old grid. It’s your go-to when you’re not mapping the real world. I’ve used it for:

  • Game Maps: Remember those old RPGs with sprawling worlds? CRS.Simple is perfect for displaying those.
  • Floor Plans: Need to show the layout of a building? This is your friend.
  • Star Charts: Mapping the cosmos? Yep, CRS.Simple can handle that too.

With CRS.Simple, you’re dealing with pixel units. No latitude, no longitude. Just a flat, infinite plane. The coordinates are in y, x order, and at zoom level 0, one coordinate unit equals one pixel. Simple, right?

The Conversion Headache: Why Things Go Wrong

The problem? CRS.EPSG3857 handles real-world coordinates and meters, while CRS.Simple lives in pixel-land. Try mixing them directly, and you’ll end up with markers in the wrong places and a map that looks… well, broken.

Real-World Scenarios and How to Fix Them

  • Mixing Data Sources: Imagine you’ve got a cool tile layer from OpenStreetMap (CRS.EPSG3857), but you also want to add data points from your own system that’s designed for CRS.Simple.

    • The Fix: You’ve got to translate those custom coordinates into latitude and longitude. Then, let Leaflet do its thing and project them onto the map. If you’ve got a formula for that translation, great! Apply it before adding the data. Otherwise, check out the Proj4Leaflet plugin. It’s a lifesaver for working with different projections.

  • Forcing CRS.Simple on Geographical Data: Trying to shoehorn real-world data into CRS.Simple?

    • Don’t! Seriously, just don’t. It’s not designed for that, and you’ll get major distortions. Use Proj4Leaflet to define a custom CRS that fits your data.

  • Custom Scales with CRS.Simple: Using CRS.Simple for a game map, but need to match it to in-game measurements?

    • The Solution: Tweak the transformation within CRS.Simple to map your coordinates to pixels. Adjust the scale and origin to match your game’s world. Here’s a snippet:

      javascript

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