Ok Martin,
I'm going to do some tests and share the results.
Thank you all for your comments and ideas.
2013/8/26 Martin Davis <[email protected]>
> This is a very interesting question. Stefan and Michael have provided
> some useful comments. Here's a little more information about the issue,
> focussing on what's in JTS today, and what could be added to improve the
> story.
>
> As you point out, there are two general approaches to this computation:
>
> 1) buffer the LIneString by the query distance and compute "contains" (or
> actually "containsProperly", which is a simpler predicate)
> 2) Compute the isWithinDistance predicate on the LineString
>
> It's hard to say which is faster *now* in JTS, and even harder to say
> which is theoretically the fastest. You'll really have to try both and
> see. Here's what's in JTS now:
>
> For #1, you should use PreparedGeometry to preprocess the buffer polygon.
> My guess is that the cost of computing the initial buffer is totally
> dominated by the query time. Then use the "cointainsProperly" predicate.
> This will utilized indexing to optimize the Point-In-Polygon computation.
> It is thread-safe now in trunk, so you may want to build from trunk and use
> that code.
>
> For #2, the current JTS isWithinDistance is not fully optimized for large
> LineStrings, since it uses a brute-force approach. Still, if the input
> LineString has a fairly low number of vertices it may still be faster than
> #1. As Michael pointed out, this can be improve by indexing the LineString
> segments using an STRtree and using the nearestNeighbour method to do a
> fast NN query. The intention is to implement this in JTS as new methods on
> the PreparedGeometry class - most of the code is done, but it still needs
> to be packaged for production.
>
> It would be very interesting to hear which of these methods turns out to
> be the fasted in your case.
>
>
>
> On Mon, Aug 26, 2013 at 10:21 AM, André Salvati <[email protected]
> > wrote:
>
>> Hi,
>>
>> I'm a beginner with JTS and this is my first post here.
>>
>> We've been working with geofences for a vehicle tracking app and I would
>> like to know what solution could give me a lower CPU consumption.
>>
>> 1) Calculate and store a Buffered Area (100 meters) from a LineString
>> object. Run 4 million times if my vehicle positions are inside or not that
>> precalculated with contains() method.
>>
>> 2) Run 4 million times isWithinDistance() method from LineString for
>> each position.
>>
>> Are there another options?
>>
>> Thanks.
>>
>>
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