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Extent for ExistingLandUseDataset

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Extent for ExistingLandUseDataset

Started by Julián DELGADO

Dear all


Late days a previous commented topic have arose due to the last clarifications from the consultation issues IR-ISDSS process: ‘extent’ attribute on ExistingLandUsedataset and SampledExistingLandUsedataset. I remember comment it during some informal discussions but I checked and there is no a formal comment in the Cluster. It is important to be commented here to reach and homogenous view on the matter.

Now in the Land Use specifications, the ‘extent’ attribute for ExistingLandUsedataset and SampledExistingLandUsedataset in is modelled like a ‘GM_MultiSurface’. This fact implies an obligation to provide the extent like a whole geometry that represents the concrete contour, vertex by vertex, of the dataset.
 
In practical sense to get this big geometry implies union and dissolve operations over all geometries in the dataset. For example in Spain we had to dissolve more than 2 million of polygons to get this precise geometry with high processing effort. And the resulting vector geometry is not really practical to be managed locally or served by WFS due to its big volume (millions of vertexes). As LU dataset has not obligation to coincide in limits with coastline, frontiers or borderlines; the traditional vector lines to define national or regional extents are not re-usable.

We remain that the objective for an extent attribute is to provide an estimated information about the place covered by the dataset. In case you need an actual or precise description of the data you can always use the layer of elements that compose the dataset (polygons, points, etc.)
To simplify the management of LU extent, we proposed to modify the ‘GM_MultiSurface’ for other simpler type, more practical and homogeneous with others themes. For example the extent for LandCoverDataset is modelled like ‘EX_Extent’ that can represent a bounding box of complete dataset, too much easy to reproduce. EX_Extent is broadly used in metadata parameters and is well known by many users, and additionally an EX_Extent can be used also in detail for that users that want to still maintaining a concrete contour vector delimitation.

At theoretical level does not mean any inconveniences for exiting implementations, but we do not know about practical implications. EX_Extent --> EX_GeographicExtent --> EX_BoundingPolygon (GM_Object, being primitive root for any geometry type, included GM_MultiSurface).

Do you have opinion about it?

Our best regards

Julián

Land Cover & Use

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