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microsoft / Uganda-Tanzania-Building-Footprints

Open dataset of machine extracted buildings in Uganda and Tanzania
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How to access imagery #13

Open adriangrepo opened 4 years ago

adriangrepo commented 4 years ago

As far as I can tell the geojson contains FeatureCollections of polygons but contains no URL links for source imagery, and no way to work out where exactly the polygons are located.

How can I access the geotiff imagery that the polygons were drawn on?

jjniev01 commented 4 years ago

In the README, the authors mention that the imagery is the composite Bing Maps imagery and specifically imagery from Maxar. Looking at the README of the related Microsoft US Buildings dataset, it would appear they are performing the extraction from the 30cm optical imagery products from Maxar/DigitalGlobe. The authors cannot share the source imagery due to the fact Maxar sells that imagery and therefore is likely under a non-distributable commercial license

Curious about the temporal specificity of the imagery myself, I did a bit of digging. Given that the initial commit of this repo was around September 20, 2019, we can assume the imagery was likely collected prior to September 2019. Using the Maxar/DigitalGlobe Image Library Explorer tool and iteratively querying (spatial query has a limit of 100,000 sq km) both Uganda and Tanzania have 30cm optical imagery available from May 2018 at the earliest. It is worth noting that there is not 100 percent coverage of Uganda and Tanzania. So we can assume the source imagery was likely collected sometime between May 2018 and August 2019 and that the extraction likely used composites in order to maximize cloud-free coverage.

Hope this is helpful.

Best, Jeremiah