Back in 2005, when Google Earth and Google Maps were launched, the public had their first taste of easily accessible satellite photography. However, two aspects went unnoticed by most users…
The first was that much of the clear and colorful imagery was not from satellites way, way out there in spaaaace - but was actually much closer, from high-flying aircraft!
Not a real satellite
While most of us were oohing and aahing over the magic of satellite (and aircraft!) imagery, we missed something else magical – that we could view our rather round planet on our very flat and square screens?
We take it for granted that maps are printed on flat paper, but when civil engineers tried using Google Earth as a background for their designs..? Well, they discovered it wasn’t so simple!
Even for quite small projects you will find it you line up one part of a satellite image with your drawing, other bits will just not line up, at all.
Because the Earth is not flat!
Around the world and throughout history this has been a problem, leading to the creation of over 3000 different map datums, projections or coordinate systems, to try to cope with this.
Map Datum or Projection, what’s the difference?
A datum is about accurately positioning a model of the Earth to match it with reality, essentially determining where and how the model sits relative to the actual Earth.
A projection is about transforming that three-dimensional reality into a useful two-dimensional depiction, deciding how best to flatten a globe onto a page or screen with the least distortion for their purpose.
Their purpose?
Yes, you see many attempts have been made to create flat maps of a round planet, such as showing it as though inside a cylinder, or as a round map based on a central point, or as a cone, or…
The thing is, it’s not really possible to lay a curved surface flat, so something has to give!
Each projection preserves some properties (e.g., area, shape, direction, or distance) while distorting others.
Hence the choice of map projection depends on the purpose of the map and the area being represented. For example, the Mercator projection is often used for navigation because it preserves direction, but it distorts the size of countries near the poles.
In contrast the Gall-Peters projection is used to compare the relative sizes of countries because it preserves area, but then it distorts shape, direction, and distance!
All of those complicated systems strive to do the same thing that Plex-Earth does simply and automatically for engineers who want to design with aerial imagery as a background, or reference.
Plex-Earth’s ‘one weird trick’ is as simple as peeling an orange…
Yes, the secret is to slice it up into smaller segments; the smaller the better!
Lambros Kaliakatsos, our Founder and CEO, explains that: “It’s a bit like peeling an orange and trying to lay the peel flat – not so easy, right? But (if) we cut the peel into smaller, manageable pieces, they lay flat perfectly.”
Not a real orange…
But Wait, There’s More!
But even that one weird trick isn’t enough - because the segments move!
While not a datum per se, the ITRF (International Terrestrial Reference Frame) provides the most precise global reference frame for Earth science applications, including the study of sea level changes, satellite orbit tracking and yes, watching the tectonic plates moving…
That’s why some datums are anchored not by Earth’s coordinates but to the biggest and nearest tectonic plate. So if the plate moves, the map datum moves with it!
For example while WGS 84 (World Geodetic System 1984) is used by Google Earth and is great for positioning or world navigation, the main datum for the USA is actually NAD 83 (North American Datum 1983). This is fixed to the North American tectonic plate, making it more stable for regional use compared to WGS 84.
How about for Europe? ETRS89 (European Terrestrial Reference System 1989) is tied to the European plate…
Is this starting to sound (even more) complicated?
Well here’s the weirdest and easiest trick of all; you can just select a specific known spot of your project on Google Earth. Easy, right?
From there you can just let Plex-Earth import, scale and perfectly align our free or premium, updated and higher-res’ satellite and aerial imagery for you, automagically!
There’s even more - it provides terrain data as well!
Try Plex-Earth today with a free trial, then play with the super-easy custom geo-referencing feature to discover just how weirdly easy it all becomes, when you’re using Plex-Earth!