ST_DFullyWithin

[Bruce Rindahl]

small type on the third query but the results are the same

On Thu, Jan 25, 2024 at 4:45 PM Bruce Rindahl <bruce.rindahl at gmail.com>
wrote:

> " I don't think that word means what you think it means"
>
> Say A is a point at 0.1,1
> B is a line from 0,0 to 0,2
>
> Then using the following code:
> --------------------------------------------------------------
> with a as (select st_makepoint(0.1,1) as geom),
> b as (select st_makeline(st_makepoint(0,0),st_makepoint(0,2)) as geom)
>
> select 'ST_Covers(ST_Buffer(A,Dist),B)',  ST_Covers(ST_Buffer(a.geom,
> 0.2), b.geom) from a,b
> union all
> select  'ST_DFullyWithin(A,B,Dist)',  ST_DFullyWithin(a.geom,b.geom,0.2)
> from a,b
> union all
> select 'ST_Covers(ST_Buffer(B,Dist),A)',  ST_Covers(ST_Buffer(b.geom,
> 0.2), b.geom) from a,b
> union all
> select  'ST_DFullyWithin(B,A,Dist)',  ST_DFullyWithin(b.geom,a.geom,0.2)
> from a,b
> -------------------------------------------------------------
>
>
> Yields:
> QUERY                                                RESULT
> "ST_Covers(ST_Buffer(A,Dist),B)"      false
> "ST_DFullyWithin(A,B,Dist)"                false
> "ST_Covers(ST_Buffer(B,Dist),A)"      true
> "ST_DFullyWithin(B,A,Dist)"                false
>
> I think the last row should also be true.
>
>
>
> On Thu, Jan 25, 2024 at 1:14 PM Paul Ramsey <pramsey at cleverelephant.ca>
> wrote:
>
>>
>>
>> On Jan 25, 2024, at 11:57 AM, Martin Davis <mtnclimb at gmail.com> wrote:
>>
>> Another reason for keeping the meaning "ST_DFullyWithin(A, B) =
>> ST_Covers(ST_Buffer(A, Dist), B)":
>>
>> I see the main use of this function in queries to be "find all the B
>> features which are fully within distance D of an A feature".  So the A
>> feature is the *constant* "query item", and it is evaluated against a set
>> of B features.  It seems more intuitive for the constant feature to be the
>> first argument in functions.
>>
>>
>> Concur, this is also my intuition, which is why it’s coded the way it is…
>>
>> P
>>
>>
>> PS note the definition needs to use Covers rather than Contains, due to
>> that ol' quirky definition of Contains!
>>
>> On Thu, Jan 25, 2024 at 10:57 AM Paul Ramsey <pramsey at cleverelephant.ca>
>> wrote:
>>
>>>
>>>
>>> On Jan 25, 2024, at 10:19 AM, Bruce Rindahl <bruce.rindahl at gmail.com>
>>> wrote:
>>>
>>> I agree with Regina.  Also why are we coding this as a function in C
>>> when it can be done either of two ways in SQL:
>>>
>>>
>>> In general functions in SQL are less fun to upgrade. Will eventually do
>>> this via Hausdorf.
>>>
>>> I don’t know that I agree about the parameter ordering, and I do not
>>> think the name of the function provides any guidance when I re-write it in
>>> object form,
>>>
>>> A.DFullyWithin(B,R)
>>>
>>> at least not in the same way that
>>>
>>> A.contains(B)
>>>
>>> makes parameter meaning clear.
>>>
>>> It’s the “D” that wrecks it.
>>>
>>
>>
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