[postgis-users] PostGIS to calculate time spent within polygon

[Simon Greener]

I haven't used the Linear referencing funcitons of PostGIS but perhaps this might help.

First find the intersection points of the measured line and the polygon using ST_Intersection. Don't worry about loosing the M in the returned data - what you want is the point at which the line enters (ST_StartPoint) and leaves (ST_EndPoint).

Then use these points and the appropriate Linear referencing functions (http://postgis.refractions.net/documentation/manual-1.4/ch07.html#Linear_Referencing) to compute the time measure values where the line enters the polygon and when it leaves.

regards
Simon

http://postgis.refractions.net/documentation/manual-1.4/ST_Line_Locate_Point.html
On Wed, 07 Oct 2009 14:19:37 +1100, George Silva <georger.silva at gmail.com> wrote:

> You can select the interval between minimun and maximum timestamp outside
> each polygon. Interpolate to get a value "when entering" the polygon
> (intersection between line and polygon) and when leaving.
>
> Then you can subtract both values to get an estimate of time.
>
> You probably can write a simple function for this.
>
> George
>
> On Tue, Oct 6, 2009 at 11:18 PM, Masanao Yajima <yajiyajijp at yahoo.co.jp>wrote:
>
>> Thank you for your response.
>>
>> However, would it be possible to elaborate on the 2nd part?
>> If my reading of the manual is correct,
>> I believe st_intersection is not implemented to handle the 4th dimension.
>>
>> Masanao Yajima
>>
>> On Tue, Oct 6, 2009 at 6:47 AM, Suhr, Ralf <Ralf.Suhr at itc-halle.de> wrote:
>>
>>>  Hello Masanao Yajima,
>>>
>>>
>>>
>>> for db-design you can go with ogr2ogr (GPX -> PostGIS). Ogr2ogr creates
>>> point and line geometrys from gpx files. In case of linestring you have to
>>> add the 4. Dimension from the point table.
>>>
>>> A optimal query would be the intersection from gps-linestrings and your
>>> polygon area. The result can be many sublinestrings with start and end time.
>>>
>>>
>>>
>>> Gr Ralf
>>>
>>>
>>>
>>> *Von:* postgis-users-bounces at postgis.refractions.net [mailto:
>>> postgis-users-bounces at postgis.refractions.net] *Im Auftrag von *Masanao
>>> Yajima
>>> *Gesendet:* Montag, 5. Oktober 2009 23:03
>>> *An:* postgis-users at postgis.refractions.net
>>> *Betreff:* [postgis-users] PostGIS to calculate time spent within polygon
>>>
>>>
>>>
>>> Dear PostGIS users
>>>
>>> I am new to PostGIS and I would like expert opinion on how to deal with my
>>> situation.
>>>
>>> I have 2D GPS data and time associated with each points and they
>>> represents line of a trip.
>>> I also have few geographic polygon data representing some area on a map.
>>>
>>> what I want to get out is length of time that is spent within polygon area
>>> for a trip.
>>>
>>> What is the optimal way to design a database and what kind of query would
>>> you use to get such a number.
>>>
>>> One constraint is the time interval for GPS is not accurate so sampling
>>> rate vary alot with in a trip.
>>>
>>> I thought of using time as 4th dimension but I believe st_intersection is
>>> not implemented on the 4th dimension..
>>>
>>> I could do this by bruit force but I am looking for something fast.
>>>
>>> I appreciate your help.
>>>
>>> --
>>> Masanao Yajima
>>>
>>> _______________________________________________
>>> postgis-users mailing list
>>> postgis-users at postgis.refractions.net
>>> http://postgis.refractions.net/mailman/listinfo/postgis-users
>>>
>>>
>>
>>
>> --
>> Masanao Yajima
>>
>> _______________________________________________
>> postgis-users mailing list
>> postgis-users at postgis.refractions.net
>> http://postgis.refractions.net/mailman/listinfo/postgis-users
>>
>>
>
>


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