Urban spot in Auvergne-Rhône-Alpes
Description
Takeover of the urban spot in the Auvergne-Rhône-Alpes region, over several years
The method is to generalise the objects of the BD Topo® database, the only large-scale vector database, following the method defined by the ex-CETE of the South West (now CEREMA) in 2008. Urban spot is defined here as urbanised areas, industrial areas or
commercial and airport areas.
The BD Topo® is a vector database of the IGN available since 2007 throughout the French territory. With a metric accuracy, it allows exploitation up to a scale of 1/10 000 or even 1/5 000.
As the Topo® BD essentially includes simple geographical objects such as buildings or sometimes areas of activity, it is necessary to obtain an urban spot to perform a mathematical morphology operation called “urban spot closure”.
This closure is the combination of two basic operations: a dilation and one, erosion.
The expansion consists of aggregating buildings that are less than D meters apart. To do this, a buffer is created from each object. The buffer is a polygon encompassing the area within a radius of R=D/2 around an object.
Erosion consists of giving back to the objects their initial size by leaving together the objects that have been aggregated. To do this, a negative “-R” radius buffer is applied.
As part of this method and following the specifications proposed by Certu in 2005 (now CEREMA), a 50-metre closure was applied to the data thus processed.
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Tags
- auvergne-rhone-alpes
- donnees-ouvertes
- ortho-imagerie