[postgis-users] Fastest test for point (nearly) in polygon

[Ben Madin]

Thanks Stephen,

that's very helpful.

cheers

Ben



On 14/12/2011, at 10:47 AM, Stephen Woodbridge wrote:

> On 12/13/2011 9:38 PM, Ben Madin wrote:
>> G'day all,
>> 
>> I'm sure I've seen a similar discussion to this question, but I can't
>> find it now. During a bulk data submission process we have a large
>> number of point locations and the code of the province in which they
>> are 'reputed' to be occurring. Having put some basic checks through
>> the system we are inclined to check this at upload time, but have to
>> realistically anticipate that points within a certain limit will be
>> adequately accurate (at the moment about 2km, but probably doesn't
>> have to be strictly 2km)
>> 
>> There are any number of ways of doing this - all uploaded data (and
>> geometries) are currently in EPSG 4283 (Australian Lat Long).
>> 
>> Options would include using :
>> 
>> st_distance_sphere(province polygon, st_setsrid(st_makepoint(long,
>> lat), 4283))<  2000
> 
> this has to compute all distances regardless
> 
>> 
>> st_dwithin (province polygon, st_setsrid(st_makepoint(long, lat),
>> 4283), 0.02)
> 
> st_dwithin() is fastest and if you need it more accurately, then:
> 
> st_dwithin(...) and st_distance_sphere(province polygon, st_setsrid(st_makepoint(long, lat), 4283))<  2000
> 
>> st_within (st_buffer(province polygon, 0.02),
>> st_setsrid(st_makepoint(long, lat), 4283))
> 
> don't buffer the polygon, always buffer the point and even faster than that use st_dwithin
> 
>> st_intersects(province polygon,
>> st_buffer(st_setsrid(st_makepoint(long, lat), 4283)))
>> 
>> or any number of similar variants.
>> 
>> Our problem is that there are many rows, and even prior to these
>> checks, other checks on other aspects of the data were inclined to
>> take longer than we would like.
>> 
>> I can accept that trying to avoid to much transforming is probably
>> better (and accepting some slightly inconsistent accuracy) from a
>> speed perspective.
>> 
>> Can anyone suggest which of these checks (or others) might be
>> fastest?
>> 
>> I'm leaning towards the latter two as they are mainly functions
>> offered by GEOS, which I understand to be faster than PL functions.
>> 
>> cheers
>> 
>> Ben
>> 
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