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

[Esteban Zimanyi]

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
>
>
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