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

[George Silva]

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
>>
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>>
>>
>
>
> --
> Masanao Yajima
>
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-- 
George R. C. Silva

Desenvolvimento em GIS
www.sextantegeo2.blogspot.com
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