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<P><FONT SIZE=2>Margie,<BR>
<BR>
This may be a dumb question on my part, but why can't you keep track of time separate from space with a datetime field and then use the numerous functions in postgresql for doing datetime overlap comparisons combined with spatial overlaps.<BR>
<BR>
Thanks,<BR>
Regina<BR>
<BR>
<BR>
-----Original Message-----<BR>
From: postgis-users-bounces@postgis.refractions.net on behalf of Margie Huntington<BR>
Sent: Mon 10/13/2008 2:08 PM<BR>
To: postgis-users@postgis.refractions.net<BR>
Subject: Re: [postgis-users] [postgis-devel] Dropped DM (Time) dimensionwith intersections<BR>
<BR>
<BR>
I think there is a miscommunication. I'm attempting to model moving objects<BR>
in the database; specifically aircraft. These aircraft have both an<BR>
altitude and time as well as the normal x- and y- components. The problem<BR>
is, I haven't found a function that will return time, the m-component. (I<BR>
can determine altitude myself since the points are linear; thus, this<BR>
omission isn't as critical.)<BR>
<BR>
I'd like to determine if aircraft maintain a safe distance from each other.<BR>
I had hoped st_expand would model a moving bounding box; but it only returns<BR>
an x-, y-geometry. The st_zmflag is 0:<BR>
<BR>
<BR>
>From my perspective, a<BR>
<BR>
shorterSegment geometry;<BR>
shorterSegmentBuffer geometry;<BR>
coorddims smallint; <BR>
<BR>
shorterSegment:= 'SRID=4326;LINESTRINGM(0 0 1.5, 10 10<BR>
2)'::geometry; <BR>
<BR>
shorterSegmentBuffer := st_expand(shorterSegment, exactdistance);<BR>
coorddims := st_zmflag(shorterSegmentBuffer); <BR>
<BR>
Same problem exists for st_intersection; only 2D geometries are returned<BR>
since the z-component is zeroed out. The st_intersection function indicates<BR>
an intersection over the entire flight path even when the aircraft are<BR>
separated by days. The M-component is critical since aircraft fly in the<BR>
same flight path; same x-, y- and z-components.<BR>
<BR>
There aren't plans to make the M-component operational for st_expand() nor<BR>
for st_intersection()? I was attempting a polygon surface only because<BR>
there isn't a 3D nor 4D bounding box that works with time.<BR>
<BR>
<BR>
Paul Ramsey-3 wrote:<BR>
><BR>
> Unfortunately, there's no such thing as a 3D polygon, except for<BR>
> trivial cases (the triangle, the shape with all Z's the same).<BR>
> Everything else is unclear on how to interpret the enclosed "plane"<BR>
> (if that is what it is) formed by an irregularly elevated boundary. So<BR>
> we can store the things, but there's really no decent way to interpret<BR>
> them in generality. For that we need the real stuff, Surfaces,<BR>
> volumes, etc.<BR>
><BR>
> I think the "low hanging fruit" is probably more the "infrastructural<BR>
> requirement". We need a 4D index. That will allow us to handle things<BR>
> like 4D time tracks and point clouds efficiently, and form the<BR>
> indexing basis for future volumetric objects.<BR>
><BR>
> P.<BR>
><BR>
> On Tue, Oct 7, 2008 at 9:44 AM, Obe, Regina <robe.dnd@cityofboston.gov><BR>
> wrote:<BR>
>> I'm not sure how low hanging the fruit :), but first off would be being<BR>
>> able<BR>
>> to do intersections and indexable ST_DWithin with 3D polygons and<BR>
>> linestrings and so forth. For example when I place a cable up on a roof I<BR>
>> need to know if I'm hitting another piece of equipment.<BR>
>><BR>
>> Higher fruit - being able to support volumetric geometries. Right now we<BR>
>> support 2d-3D polygons and lines and you can form wireframes with those,<BR>
>> but<BR>
>> no true volumetric stuff. But then what do I know, I'm just parroting<BR>
>> things I've heard in whispers and those whispers are getting louder is<BR>
>> all<BR>
>> :)<BR>
>><BR>
>> There is still the issue of being able to display 3-D geometries without<BR>
>> spending a fortune on proprietary stuff which is not a PostGIS issue, but<BR>
>> has to gain in momentum to make PostGIS 3D more powerful (e.g. uDig for<BR>
>> 3D<BR>
>> or OpenJump for 3D or OpenLayers for 3D?)<BR>
>><BR>
>> Thanks,<BR>
>> Regina<BR>
>> ________________________________<BR>
>> From: postgis-devel-bounces@postgis.refractions.net on behalf of Paul<BR>
>> Ramsey<BR>
>> Sent: Tue 10/7/2008 12:30 PM<BR>
>> To: PostGIS Development Discussion<BR>
>> Subject: Re: [postgis-devel] Dropped DM (Time) dimension with<BR>
>> intersections<BR>
>><BR>
>> Perhaps elabourate on what better 3D support would be? There's the<BR>
>> surface object hanging around. There's the issue of maintaining higher<BR>
>> dimensional coordinates through lower dimensional transforms (which<BR>
>> you saw the result of a few days ago). There's elabourating the<BR>
>> complete set of 3D objects and relationships (gulp).<BR>
>><BR>
>> It's not clear to me what is the "low hanging fruit" that will make 3D<BR>
>> users happiest in the shortest time.<BR>
>><BR>
>> P.<BR>
>><BR>
>> On Tue, Oct 7, 2008 at 8:54 AM, Obe, Regina <robe.dnd@cityofboston.gov><BR>
>> wrote:<BR>
>>> Margie,<BR>
>>><BR>
>>> Unfortunately I think the answer is no. Most of the work going on in<BR>
>>> 1.4<BR>
>>> is<BR>
>>> to improve speed of existing functionality and reorganize the source to<BR>
>>> make<BR>
>>> it more maintainable.<BR>
>>><BR>
>>> Someone please correct me if I am wrong.<BR>
>>><BR>
>>> I for one would be very elated if we had better 3D support since CityGML<BR>
>>> and<BR>
>>> similar initiatives are becoming more of a hot topic around here.<BR>
>>><BR>
>>> Thanks,<BR>
>>> Regina<BR>
>>> ________________________________<BR>
>>> From: postgis-devel-bounces@postgis.refractions.net<BR>
>>> [<A HREF="mailto:postgis-devel-bounces@postgis.refractions.net">mailto:postgis-devel-bounces@postgis.refractions.net</A>] On Behalf Of<BR>
>>> Huntington, Margaret (US SSA)<BR>
>>> Sent: Tuesday, October 07, 2008 11:47 AM<BR>
>>> To: postgis-devel@postgis.refractions.net<BR>
>>> Subject: [postgis-devel] Dropped DM (Time) dimension with intersections<BR>
>>><BR>
>>> Hello,<BR>
>>><BR>
>>> Currently I'm using PostGIS 1.3.3. From past discussions and from<BR>
>>> testing, both the st_intersection st_extend methods return 2D results<BR>
>>> with<BR>
>>> 4D input geometries. As a temporary work-around, I had hoped<BR>
>>> st_intersection might work with 3DM geometries. (Plan was to<BR>
>>> interpolate<BR>
>>> the altitude value within the function call if PostGIS could calculate<BR>
>>> the<BR>
>>> time dimension). I found time components are also dropped by<BR>
>>> st_intersection with 3DM geometries. I abandoned usage of 4D bounding<BR>
>>> boxes<BR>
>>> since these too effectively degrade 4D geometries down to 2D geometries<BR>
>>> (altitude and time are zeroed out).<BR>
>>><BR>
>>> polyGeometry geometry;<BR>
>>><BR>
>>> bbGeometry geometry;<BR>
>>><BR>
>>> intersectionGeometry geometry;<BR>
>>><BR>
>>> coorddims smallint;<BR>
>>><BR>
>>> -- both polygon and linestring have an expected zmflag value<BR>
>>> of<BR>
>>> 1<BR>
>>><BR>
>>> polyGeometry := 'SRID=4326;POLYGONM((0 0 0, 0 10 4, 10 10 4,<BR>
>>> 10<BR>
>>> 0<BR>
>>> 0, 0 0 0))'::geometry;<BR>
>>><BR>
>>> bbGeometry := 'SRID=4326;LINESTRINGM(0 0 1.5, 10 10<BR>
>>> 2)'::geometry;<BR>
>>><BR>
>>> intersectionGeometry := st_intersection(polyGeometry,<BR>
>>> bbGeometry);<BR>
>>><BR>
>>> -- st_intersection method drops the time dimension; zmflag<BR>
>>> value<BR>
>>> of 0<BR>
>>><BR>
>>> coorddims := st_zmflag(intersectionGeometry);<BR>
>>><BR>
>>> If I were to download the subversion snapshot, the current 1.4 version,<BR>
>>> might st_intersection work with either 3DM or 4D geometries? Are<BR>
>>> bounding<BR>
>>> boxed or st_extend improved for either 3DM or 4D geometries? I had<BR>
>>> incorporated polygons only as a possible work-around to the bounding box<BR>
>>> and<BR>
>>> st_extend 2D limitations.<BR>
>>><BR>
>>> Margie<BR>
>>><BR>
>>> ________________________________<BR>
>>><BR>
>>> The substance of this message, including any attachments, may be<BR>
>>> confidential, legally privileged and/or exempt from disclosure pursuant<BR>
>>> to<BR>
>>> Massachusetts law. It is intended solely for the addressee. If you<BR>
>>> received<BR>
>>> this in error, please contact the sender and delete the material from<BR>
>>> any<BR>
>>> computer.<BR>
>>><BR>
>>> ________________________________<BR>
>>><BR>
>>> Help make the earth a greener place. If at all possible resist printing<BR>
>>> this<BR>
>>> email and join us in saving paper.<BR>
>>><BR>
>>> _______________________________________________<BR>
>>> postgis-devel mailing list<BR>
>>> postgis-devel@postgis.refractions.net<BR>
>>> <A HREF="http://postgis.refractions.net/mailman/listinfo/postgis-devel">http://postgis.refractions.net/mailman/listinfo/postgis-devel</A><BR>
>>><BR>
>>><BR>
>> _______________________________________________<BR>
>> postgis-devel mailing list<BR>
>> postgis-devel@postgis.refractions.net<BR>
>> <A HREF="http://postgis.refractions.net/mailman/listinfo/postgis-devel">http://postgis.refractions.net/mailman/listinfo/postgis-devel</A><BR>
>><BR>
>> ________________________________<BR>
>><BR>
>> The substance of this message, including any attachments, may be<BR>
>> confidential, legally privileged and/or exempt from disclosure pursuant<BR>
>> to<BR>
>> Massachusetts law. It is intended solely for the addressee. If you<BR>
>> received<BR>
>> this in error, please contact the sender and delete the material from any<BR>
>> computer.<BR>
>><BR>
>> ________________________________<BR>
>><BR>
>> Help make the earth a greener place. If at all possible resist printing<BR>
>> this<BR>
>> email and join us in saving paper.<BR>
>><BR>
>> _______________________________________________<BR>
>> postgis-devel mailing list<BR>
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>><BR>
>><BR>
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