Monitoring cadastral changes in near real-time: future or reality?
It is way too often that the cadastral information (building footprints, roads, parcel boundaries, etc.) seen on online maps (Google, Bing, etc.) is thought of as reflecting the current state of our environment. Indeed, they provide a tremendous amount of information and Google stands quite over the crowd in terms of displayed features (Google maps vs. Apple maps: How far ahead of Apple Maps is Google Maps? https://www.justinobeirne.com/google-maps-moat). However, have you ever wondered about the date of the data displayed? You can sometimes see the year of acquisition in the “Acknowledgement” bar at the bottom of the map, but this does not ensure neither that that all the data present is up to date, nor that it is complete.
Did I miss changes?
Let’s have a look at a concrete example. The screenshots hereafter presents a part of the city of Thayngen in Switzerland, as seen in Google Earth and Google maps.
Interestingly, the “Acknowledgement” is “Map data © 2018 GeoBasis-DE/BKG” on Google map and Google Earth. However, as we will see later, the map and images are missing a newly built building finished in the summer 2017, right south of the railways and the industrial zone.
On the side of Bing maps and its satellite imagery, the situation is similar: Acknowledgement of this year “© 2018 HERE, © OpenStreetMap” but the new building is still missing.
Considering that Switzerland is often at the cutting edge of geo-information, one would think this building would be found in the cadastral geoportal (in this case of Canton Schaffausen). But here again, we got out-dated information and there is no sign of the building built a year ago. None to blame, the time it takes to survey the zone and report it to the city/canton can easily take up to half a year. Then updating the information online can take even more months, resulting in almost a full year of delay. Actually, the new building was added very recently on the geoportal (see at bottom the screenshot from july).
Sentinel at the rescue!
From 2015 on, the European Comission together with the European Space Agency have launched a serie of satellites called Sentinels. These satellites are opening new horizons for two main reasons: 1) their data is open access for free and 2) their revisit time (frequency of new data over a given location) is extremely short, with an average of a new image every three days over Europe.
The general trend of Earth observation satellite is moving towards daily data acquisition over the entire globe enabling near-real time applications. States pave the way while the private sector follows closely with companies operating (currently or in the near future) satellite constellations such as Planet (labs), Earth.i, Spire, Satellogic, Urthecast and many others.
The Sentinel-2 satellite with its high frequency could enable the detection of cadastral changes, such as monitoring this construction site and tracking the evolution of a building as it is being constructed.
Picterra has recently integrated a monitoring tool on its platform (https://app.picterra.ch) to address the ever rising importance of monitoring land surface changes. With it, we could spot the beginning of the building construction in March 2017 and monitor its evolution until July 2017 where most of the building was finished.
Finally the detected newly built building could be processed for extracting its footprint and exported to any Geographic Information System or to update OpenStreetMap.
So stay tuned for more and if you have any questions feel free to contact us at http://www.picterra.ch
