Today, satellite imagery is one of the most popular features of Google maps. Capturing the world from above is a laborious task that aims to match millions of images to precise locations. But how do satellite images actually work? How often are these images updated? What are the biggest challenges in bringing satellite imagery to over a billion users?
The mosaic of aerial and satellite photographs that you can see in Google maps and Google earth comes from many different suppliers including state agencies, geological service organizations and commercial image providers. These images are taken on different dates and in different lighting and weather conditions.
Google earth is the platform that lets you explore over 36 million square miles (1mi² = 2.59km²) high-definition satellite images from various vendors, covering over 98% of the total population, to see the world from above. While these stunning photos show us parts of the world we might never get the chance to visit, they also help Google Maps accurately model a world that changes every day.
There is a whole industry around aerial surveys. Companies install devices under planes and cameras take pictures as they fly over the target. In many parts of the world this is happening all the time.
In places where a market for aerial surveys has not been established, satellites are used. With aerial surveys, you get very high quality images sharp enough to create detailed maps. Satellites produce lower quality images, but they are still useful because they provide worldwide coverage.
Google obtains commercially available satellite images from different vendors, and their team assembles the images to create a perfect map. This is a process called photogrammetry which is being automated via the machine learning to help accurately position images and improve resolution.
These images show us extremely important details about an area, such as roads, ground markings, buildings and rivers, as well as the precise distance between each of these objects. All this information is collected without the need to set foot on the place itself.
By perfecting the technique of photogrammetry over the past 10 years, Google can align images from multiple sources (Street view, aerial and satellite images, as well as authoritative datasets) with accuracy up to one meter.
Over the past 15 years, Google has provided maps in more than 220 countries and territories and displays useful information for more than 200 million places.
How often do you update satellite images?
Google’s goal is update satellite images of places that change the most. For example, because big cities are constantly changing, they try to update satellite images every year. For mid-sized cities, they update the images every two years and every third for smaller cities.
The general goal is to keep densely populated places regularly updated and to keep up with a changing world, so that the areas are updated more frequently considering that there are many buildings or road construction. In progress.
Why do we sometimes see mysterious objects on maps?
Google engineers explain that sometimes the way images are collected can create optical illusions. One of the most common cases is that of “sunken ships”, which are actually sailboats that can appear underwater due to the way satellite images are grouped into layers. Other times, the sunlight can reflect something bright, and it will look like a strange white object that some identify with haunted houses or other spooky things.
Card creation never ends and work is constantly being done to create new tools and techniques to make collecting images faster, more accurate and safer for everyone.