I think it's good when CF files can be interpreted, ideally both by humans and
computers, and ideally unambiguously. That means it should be easy, for
example, to color in in the five pointed star posted by @davidhassell above,
which region should be used for averaging over this geometry. It
Closed #354.
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The role of CF is rules for metadata, which is mainly labeling and data
structures. CF should try to stay within that role and avoid content details,
notwithstanding the current complexity of section 7.5. Geometry consistency
and compatibility is well addressed by other conventions. CF
My experience of spatial databases (Oracle Spatial about 5 years ago) is that
self-intersections caused the geometry to be tagged as invalid forcing it to be
constructed from a collection of simple polygons. Geometries need to work with
established tools which will dictate any standards.
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We have lots and lots of polygons with self intersections where the polygon
closes on itself at a node. It may not cross but it does need to pinch off an
open back up -- so an intersection is real.
I don't think CF should have a horse in this race.
There certainly are ways to interpret self-intersecting polygons in a
consistent manner. But is there a use-case for this in the realm of CF? For
self-intersecting lines, this seems clear (any kind of route, for instance,
from ships, planes, etc.), but for polygons, I struggle. Hence my
I think that the main implication of allowing self intersecting edges of a
polygon (like the possibly 5, probably 2 1/2 sided polygon from @davidhassell
above) is people may use the wrong inside/outside algorithms and get unexpected
results.
The main ones are left-hand/right-hand, winding
Hello,
I agree with Dave that there are no rules on that, but I'd like to fully
understand what you are suggesting for polygons. Do you mean "are different
_parts_ of a multi-part polygon allowed to overlap" or do you mean "are
different _edges_ of an individual polygon part allowed to
>From my recollection, there are no rules on topology in the spec, so yes. Self
>intersections are fine.
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In CF Conventions section 7.5 a number of cases for geometries are supplied.
Are "line" and "polygon" geometries as well as individual multipart analogs
allowed to self-intersect themselves?
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