Can I assume that the inner points of the buffer are identical to the outer points of the source polygon?
From: Martin Davis [mailto:[email protected]] Sent: Monday, October 26, 2015 4:27 PM To: Jeff Dege Cc: [email protected] Subject: Re: [Jts-topo-suite-user] Rounding error gaps with buffers? 1. The returned value from the Geometry.buffer method contains only the buffer polygon. 2. If you use a "large enough" buffer distance the buffer polygon should properly contain the input polygon. And the "large enough" distance can be quite small, since double precision is used during computation. If you want to try out how JTS responds to your inputs, I suggest installing the product and using the JST TestBuilder to try things out. Martin On Mon, Oct 26, 2015 at 2:01 PM, Jeff Dege <[email protected]<mailto:[email protected]>> wrote: We have a problem where we need to draw areas on a map that only slightly overlap. This is used in a routing application, where events are assigned to the assigned user for each area. What we want is to have the areas overlap slightly, so as to avoid any possibility of there being a gap. For us to have a small area along the border between two areas in which which user the event is assigned to is acceptable. For us to have even the smallest area in which an event might fall between the cracks is not. Given my understanding of floating point rounding errors, it’s not possible to have absolute equality. If you’re going to avoid any cracks, you’re going to have to have some overlap. What we’re envisioning is to have a newly drawn area clip against the existing area, and then to expand the newly drawn area slightly. We’re considering the JTS Topology Suite. It looks as if its Buffer functionality might do what we need. But before we install it and try to work with it, we have a few questions: 1. When I create a buffer around a polygon or multipolygon, does the geometry that it returns contain the buffer plus the polygon, or just the buffer? 2. If the returned geometry contains just the buffer, will a union of the buffer with the original polygon never contain holes along the boundary, due to floating point rounding errors?
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