Andy Turner a écrit :
> my understanding is that in querying a continuous coverage a method should in
> principal be able to return a value that is not a no data value (null) at any
> point in its domain (...snip...). In querying a discrete coverage we can
> expect null returns within the envelope. for some points, but that depends on
> how the boundaries of two discrete parts of the coverage are defined. I don't
> know if it is allowed to return more than one value for a discrete coverage
> which might be the case at a boundary, or if the discrete parts of the
> coverage are allowed to overlap.
I don't think that the difference between discrete and continuous coverage is
about returning null (nodata) values or not. I think that the difference is
rather that DiscreteCoverage do not applies interpolation. evaluate(point)
returns the same value for every point inside a pixel, no matter if the point
is
at the pixel center or near the corner of that pixel. On the contrary,
ContinuousCoverage can apply an interpolation, so that requerying the value at
the center or near the corner of a pixel will produce different values.
Whatever
that pixel represents a "nodata" value is an other topic.
I think that overlapping objects are allowed in discrete coverages.
Martin
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