[Mobilitydb-users] Query regarding intersection of a temporal point with Z dimension and polygon

[Sharath S Bhargav]

Hello Esteban,

Apologies for late reply.
Would this work if the polygon also defined in 3 dimensions? As in if it
was a pure 3 dimensional operation.

On Tue, Mar 16, 2021 at 4:52 PM Esteban Zimanyi <estebanzimanyi at gmail.com>
wrote:

> Dear Sharath
>
> I created a small example to see whether it fits your requirements. In my
> local working copy of MobilityDB I enabled the operations on mixed 2D and
> 3D geometries (currently disallowed in MobilityDB). The example looks as
> follows.
>
> select astext(atGeometry(tgeompoint '[Point(0 0 0)@2000-01-01, Point(4 4
> 4)@2000-01-05]', geometry 'Polygon((1 1,1 2,2 2,2 1,1 1))'));
>                                        astext
>
> ------------------------------------------------------------------------------------
>  {[POINT Z (1 1 1)@2000-01-02 00:00:00+01, POINT Z (2 2 2)@2000-01-03
> 00:00:00+01]}
> (1 row)
>
> Does this correspond to your requirements ?
>
> Esteban
>
>
> On Sat, Mar 13, 2021 at 4:56 AM Sharath S Bhargav <
> shrthsbhargav96 at gmail.com> wrote:
>
>> Hello Esteban,
>>
>> The method st_3DIntersection is required for true 3D intersection. While
>> st_intersection does return results with points having 3 dimensions by
>> averaging the Z dimension value. But the results returned from MobilityDB
>> seem to indicate that is also not supported since I get a tbool with only
>> false values. Can I assume that MobilityDB does not support 3 dimensions in
>> any of the intersection functions even in a 2.5D fashion?
>> If the tintersect function could return true by just considering the 2
>> dimensions of the trajectory and average out the Z dimension that would
>> also work for me. I expected this behaviour since MobilityDB delegates the
>> spatial calculations to PostGIS and PostGIS does actually do the same and
>> return the intersecting line string as shown in the query example. So
>> considering PostGIS response, I was hoping MobilityDB could return a true
>> period set. It would be great if you could kindly clarify the behaviour in
>> this scenario. Apologies if I seem to be asking trivial questions, I am new
>> to the Spatio-Temporal Databases.
>>
>> On Sat, Mar 13, 2021 at 3:14 AM Esteban Zimanyi <estebanzimanyi at gmail.com>
>> wrote:
>>
>>> Dear Sharath
>>>
>>> As I mentioned before, MobilityDB delegates to PostGIS the calculation
>>> of the spatial operations. According to what you described, to implement
>>> your scenario you require to use the PostGIS method ST_3DIntersection
>>> https://postgis.net/docs/ST_3DIntersection.html
>>> It is stated in the above link that this method needs SFCGAL backend.
>>>
>>> We have never used MobilityDB together with SFCGAL. We could envision
>>> starting this exploration in the future, but currently we have many other
>>> things in the development pipeline of MobilityDB.
>>>
>>> If you want to start this exploration, we could provide you guidance in
>>> this regard and depending on our availability, we can also extend
>>> MobilityDB to make this happen.
>>>
>>> Esteban
>>>
>>>
>>
>> --
>> Regards,
>> Sharath
>>
>>

-- 
Regards,
Sharath
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