Historical images are a priceless source of geographic data, they recorded the past landscape with a high resolution when satellite images were not available. Unfortunately, at this time, GPS geotags did not exist either. As a result, the only geographic information about historical images is generally an ambiguous place name which is not sufficient to properly register the images and extract their geographic content.
smapshot uses the power of the crowd to accurately georeference the images in a virtual globe. The virtual globe is fed by 3D data from the Swiss Federal Office for Topography. To georeference an image, the volunteers have to click on similar points in the image and in the virtual globe. These 2D-3D correspondences are the well known Ground Control Points (GCP) required in photogrammetry to compute an image’s orientation.
Digitisation of the 2D-3D correspondences in smapshot
When an image is georeferenced, it is inserted as a 3D object in the virtual globe. There is a two-step validation. First, an error on each GCP is computed, if the maximal error is above a threshold, the geolocalization can’t be validated by the volunteer. Second, the archivists who provide us with the images check visually the alignment. In this way, they ensure that the geographic metadata extracted such as the exact 3D image location and orientation, the image footprint and the place names that are visible in the image will be accurate.
After this process, the visitors can interactively compare the current virtual landscape with its historical state. This functionality is essential for the visitors to visualize the impact of urbanization or climate change during the last 150 years. The georeference is also essential for archivists who gain valuable geographic information.
Currently, 12 images collections are published on the platform and more than 17’000 images were georeferenced by the crowd.
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Google is hailing it as ‘one of the most requested features for Google Earth’ and we can just see why. The shiny new Measure Tool, which rolled out for Android and Chrome this week, lets you measure the distance between any two points on the planet. Not just that, you can also measure the surface area of any piece of land of your choice on Google Earth.
Here’s how it works: Fire up Google Earth on your browser or phone and you will be greeted by a small ‘ruler’ icon in the menu bar. Zoom into the map, click on any two points you want to know the distance for, and let Measure Tool take care of the rest.
So, if you want to know the length of your favorite hiking trail, this would be a good place to find that out. Or if you have always wondered what the distance between Timbuktu and Tokyo is, Google Earth’s got you covered:
Even cooler is measuring the area of things like parks, stadiums, lakes, etc. The tool lets you select the borders of any shape – regular, irregular – by connecting the dots. In the image below, Google shows you how you can measure the area of the park in a locality you are interested in:
We can imagine this tool becoming pretty handy for students and academicians. For example, teachers can use Measure to create clever math problems for students, like finding out which is bigger: Colorado or Utah?
Measure Tool sure is channeling our inner nerd, and we are hoping Google rolls out the iOS update for it soon. So, what are you going to measure today?
