Understanding Coordinate Systems and Map Projections

Drone surveying is easy to understand with some hands-on experience and training. Learning to fly the Phantom 4 RTK only takes a couple hours, and getting your Part 107 is way easier than you think. Operating smart GCPs like AeroPoints take one button. 

But when you get into coordinate systems and map projections, things can get complicated. 

We want to break it all down for you. Here, we’ll cover the basics of coordinate systems and map projections so you can understand why they’re necessary for accurate maps. Plus, we’ll explain why transforming between different coordinate systems is necessary. 

What is a coordinate system?

When you see the term coordinate system, it’s referring to what’s more precisely called a coordinate reference system. It’s a system that defines the location of a point on a plane or sphere. 

Think of it this way: coordinate systems provide X, Y, Z, locations for all points in space. Knowing this information lets you determine where you (or your worksite) are on the earth. 

Image via Wikimedia Commons/djexplo

The two kinds: geographic and projected coordinate systems

Technically, there are two classes of coordinate reference systems: geographic and projected coordinate systems. 

Geographic coordinate systems are three-dimensional grids, while projected systems use map projections to view the world in 2D. National and local grids—two things you’re probably familiar with—are projected coordinate systems. 

Projected coordinate systems can be more useful for worksites over geographic coordinate systems because they have less local distortion. For example, some local grids are only the size of a single site, which reduces projection distortion considerably.

Distortion can happen in angle, area, direction, or distance because it’s impossible to flatten a spherical surface (like the earth’s terrain), which we’ll get into more below. When picking a coordinate system to use, people choose the one best suited to their purpose. 

How coordinate systems get chosen for a worksite

There are many geographic and projected coordinate systems in use all over the world. One was picked for your worksite. 

This choice was made by the surveyor who set up the site before any building was started. Usually hired by a project owner, the surveyor uses their expertise to determine the best system to use for the worksite’s location. Once that is set, all work must be done in that coordinate system going forward. 

What is a map projection?

A map projection is defined as a systematic transformation of the coordinates (latitude and longitude) on the surface of a sphere (or ellipsoid) into coordinates on a flat plane (x, y). 

Planet Earth is spherical. It exists in three dimensions. But it’d be annoying to carry a globe around with you everywhere if you need a map. To represent our 3D earth with an accurate scale on 2D paper (or screen), we use map projections. 

The cost of this transformation means somethings are distorted. In fact, all 2D world maps are wrong in some way. (In fact, a sphere’s surface cannot be represented on a flat surface without distortion.) 

projected coordinate system

One distortion seen on common world maps is the relative scale of land masses. (Psst, Greenland isn’t actually that big.)

The world uses many coordinate systems. Here’s why. 

Now, we’ve explained what coordinate systems are, but you might wonder why so many exist. The answer? Accuracy. 

Due to the uneven sphere of the earth, shifting continents, and more, a single coordinate system for everyone isn’t a good idea if you want accurate maps. (For a deep-dive into why coordinate systems matter, check out our post.) 

Geoid undulation in false color, shaded relief and vertical exaggeration (10000 scale factor).

That means surveyors setting up worksites choose between different published coordinate systems, depending on their location, or use a local grid system. 

Here’s the rub: getting drone data, which is collected in the geographic coordinate reference system WGS84, to align with the coordinate system you use on your site means you have to transform between different systems. 

Transforming between different coordinate systems is hard, but necessary

GPS-based survey tools return data in geographic coordinate systems. This makes converting your data from one system to another mandatory. Understanding these transformations is hugely important when creating accurate surveys.

coordinate systems online converter

Transformation is a complicated mathematical process involving trigonometry, vector algebra and some more exotic math. Sometimes transformation even means bringing two disparate coordinate reference system into a third system and going forward from there.  

As you can imagine, this is a very complex and complicated process that not everyone has the knowledge to do. There are a number of different software programs that help with the process. Some only convert from very specific systems to other specific systems.

In our mission to make using site survey data easier, we at Propeller have built a handy coordinate converter to use whenever you need. It doesn’t require advanced training to operate and will save you time, so you can get back to your actual job. 

Stop doing complicated coordinate system transformations on your own. Use Propeller’s new coordinates converter today!

free online coordinates converter

 



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Crunching Drone Data: How Propeller Handles Complex Datasets

Local Grid Explained: How Propeller Can Help You Deliver Your Site Data in Local Coordinates

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