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haven't looked at MobilityDB (although I will now). In addition to PostGIS I'm using TimeScaleDB to build "continuous aggregates" of the GPS data in order to get things like the latest position per hour, the average speed per day etc. It's pretty handy for
that but is unable to use more complex aggregates with window functions, distinct, trajectory creation etc. </span><br>
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<span style="color: rgb(0, 0, 0); font-family: "Segoe UI", "Segoe UI Web (West European)", "Segoe UI", -apple-system, BlinkMacSystemFont, Roboto, "Helvetica Neue", sans-serif; font-size: 14px; background-color: rgb(255, 255, 255); display: inline !important;">I
suppose the main part of my query would be portion that distributes the difference between the lead/lag and current event_times (time delta) over the grids that the lead/lag created line pass over:</span></div>
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<span style="color: rgb(0, 0, 0); font-family: "Segoe UI", "Segoe UI Web (West European)", "Segoe UI", -apple-system, BlinkMacSystemFont, Roboto, "Helvetica Neue", sans-serif; font-size: 14px; background-color: rgb(255, 255, 255); display: inline !important;">
sum(((st_length(st_intersection(traj.traj, grid.geom)) * traj.time_delta) / traj.traj_dist))<br>
</span></div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0); background-color: rgb(255, 255, 255);">
<span style="color: rgb(0, 0, 0); font-family: "Segoe UI", "Segoe UI Web (West European)", "Segoe UI", -apple-system, BlinkMacSystemFont, Roboto, "Helvetica Neue", sans-serif; font-size: 14px; background-color: rgb(255, 255, 255); display: inline !important;">Does
MobilityDB have a function that could help with this? </span></div>
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</span></div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0); background-color: rgb(255, 255, 255);">
<span style="color: rgb(0, 0, 0); font-family: "Segoe UI", "Segoe UI Web (West European)", "Segoe UI", -apple-system, BlinkMacSystemFont, Roboto, "Helvetica Neue", sans-serif; font-size: 14px; background-color: rgb(255, 255, 255); display: inline !important;">I
tried to stay away from using the trajectory data type since it is only (x,y,t) and what I really need is (x,y,t,m1,m2,m3....) so that I can distribute the speed/bearing/dataX over the hexagon weighted with the time associated with each vertex.</span></div>
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<span style="color: rgb(0, 0, 0); font-family: "Segoe UI", "Segoe UI Web (West European)", "Segoe UI", -apple-system, BlinkMacSystemFont, Roboto, "Helvetica Neue", sans-serif; font-size: 14px; background-color: rgb(255, 255, 255); display: inline !important;"><br>
</span></div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0); background-color: rgb(255, 255, 255);">
<span style="color: rgb(0, 0, 0); font-family: "Segoe UI", "Segoe UI Web (West European)", "Segoe UI", -apple-system, BlinkMacSystemFont, Roboto, "Helvetica Neue", sans-serif; font-size: 14px; background-color: rgb(255, 255, 255); display: inline !important;">Regards,</span></div>
<div style="color: rgb(0, 0, 0); background-color: rgb(255, 255, 255);"><span style="font-size: 14px;">Rory</span></div>
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<br>
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<div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" color="#000000" style="font-size: 11pt;"><b>From:</b> Florian Nadler <florian.nadler@cybertec.at><br>
<b>Sent:</b> 24 February 2022 07:45<br>
<b>To:</b> PostGIS Users Discussion <postgis-users@lists.osgeo.org>; Rory Meyer <rory.meyer@VLIZ.be><br>
<b>Subject:</b> Re: [postgis-users] Non-linear time cost; please suggest a better way to structure the query</font>
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<p style="margin-top: 0px; margin-bottom: 0px;">Hi, <br>
</p>
<p style="margin-top: 0px; margin-bottom: 0px;"><br>
</p>
<p style="margin-top: 0px; margin-bottom: 0px;">apart from Paul advice did you ever take into consideration to use MobilityDB for this kind of spatial questions?</p>
<p style="margin-top: 0px; margin-bottom: 0px;"><br>
This will imply creating trajectories out of gps points too, but might simplify query design and processing time as this extension is developed for this kind of queries.
<br>
</p>
<p style="margin-top: 0px; margin-bottom: 0px;"><br>
</p>
<p style="margin-top: 0px; margin-bottom: 0px;">Checkout <a class="x_moz-txt-link-freetext" href="https://docs.mobilitydb.com/MobilityDB-BerlinMOD/master/mobilitydb-berlinmod.pdf">
https://docs.mobilitydb.com/MobilityDB-BerlinMOD/master/mobilitydb-berlinmod.pdf</a>, chapter 3.3 which deals with quite simliar analysis.<br>
</p>
<p style="margin-top: 0px; margin-bottom: 0px;"><br>
</p>
<p style="margin-top: 0px; margin-bottom: 0px;">Florian<br>
</p>
<p style="margin-top: 0px; margin-bottom: 0px;"><br>
</p>
<div class="x_moz-cite-prefix">Am 23.02.2022 um 15:14 schrieb Rory Meyer:<br>
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Afternoon all,</div>
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<br>
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<div style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0); background-color: rgb(255, 255, 255);">
I've got a database full of GPS points (along with associated data like speed, bearing, time, GPS_ID, class etc) and I'm trying to do complex aggregations with the data. I'm trying to build up a "heatmap" of the data by first creating a grid of polygons using ST_HexagonGrid
and then using a window function to overlay the lines (created from a lead/lag window of each GPS point and the next one from the same GPS_ID) over the grid. I'd like to get the the number of seconds that gps carrying vehicles spend in each hex cell, grouped
by class, speed, date, direction etc etc. The end goal would be to query a lon/lat and get a bunch of aggregated data for different classes, speed/bearing distributions. </div>
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<br>
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Here's a simplified look at the SQL (sorry, it's not really simple...):</div>
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'''</div>
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SELECT
<div> grid.gid,</div>
<div> grid.geom,</div>
<div> avg(traj.bearing, 511.0) AS avg_bearing,</div>
<div> avg(traj.time_delta) AS avg_time_delta,</div>
<div> sum(((st_length(st_intersection(traj.traj, grid.geom)) * traj.time_delta) / traj.traj_dist)) AS cum_time_in_grid</div>
<div>FROM (</div>
<div>(my_hex_grid AS grid LEFT JOIN ( SELECT</div>
<div> subquery.gps_id,</div>
<div><span style="color: rgb(0, 0, 0); background-color: rgb(255, 255, 255); display: inline !important;"> </span>subquery.event_date,</div>
<div><span style="color: rgb(0, 0, 0); background-color: rgb(255, 255, 255); display: inline !important;"> </span>subquery.bearing,
</div>
<div><span style="color: rgb(0, 0, 0); background-color: rgb(255, 255, 255); display: inline !important;"> </span>subquery.time_delta,</div>
<div><span style="color: rgb(0, 0, 0); background-color: rgb(255, 255, 255); display: inline !important;"> </span>st_makeline(subquery.pos, subquery.pos2) AS traj,</div>
<div><span style="color: rgb(0, 0, 0); background-color: rgb(255, 255, 255); display: inline !important;"> </span>st_distance(subquery.pos, subquery.pos2) AS traj_dist</div>
<div><span style="color: rgb(0, 0, 0); background-color: rgb(255, 255, 255); display: inline !important;"> </span>FROM ( </div>
<div><span style="color: rgb(0, 0, 0); background-color: rgb(255, 255, 255); display: inline !important;"> </span>SELECT </div>
<div><span style="color: rgb(0, 0, 0); background-color: rgb(255, 255, 255); display: inline !important;"> </span>gps.mmsi,</div>
<div><span style="color: rgb(0, 0, 0); background-color: rgb(255, 255, 255); display: inline !important;"> </span>date_part('epoch'::text, (lead(gps.event_time) OVER time_order - gps.event_time)) AS
<span style="color: rgb(0, 0, 0); background-color: rgb(255, 255, 255); display: inline !important;">
</span>time_delta,</div>
<div><span style="color: rgb(0, 0, 0); background-color: rgb(255, 255, 255); display: inline !important;"> </span>gps.geom,</div>
<div><span style="color: rgb(0, 0, 0); background-color: rgb(255, 255, 255); display: inline !important;"> </span>gps.bearing,</div>
<div><span style="color: rgb(0, 0, 0); background-color: rgb(255, 255, 255); display: inline !important;"> </span>lead(gps.geom) OVER time_order AS geom2</div>
<div><span style="color: rgb(0, 0, 0); background-color: rgb(255, 255, 255); display: inline !important;"> </span> FROM gps</div>
<div><span style="color: rgb(0, 0, 0); background-color: rgb(255, 255, 255); display: inline !important;"> </span>WHERE ((gps.event_time >= '<Start Time>') AND (gps.event_time <= '<End Time>'))</div>
<div><span style="color: rgb(0, 0, 0); background-color: rgb(255, 255, 255); display: inline !important;"> </span>WINDOW time_order AS (PARTITION BY gps.gps_id ORDER BY gps.event_time)) as subquery</div>
<div> ON (st_intersects(gps.traj, grid.geom)))</div>
GROUP BY grid.gid, grid.geom</div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0); background-color: rgb(255, 255, 255);">
'''</div>
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<br>
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<div style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0); background-color: rgb(255, 255, 255);">
My issue is that I've got a non-linear increase in time that the query takes to complete. If <Start Time> to <End Time> is a couple of hours then it's takes a couple of seconds to run. If it's for a day, it takes a couple minutes to run. If it's for a week
it takes a couple of hours. </div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0); background-color: rgb(255, 255, 255);">
<br>
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I'd like to run this for over a year of data but that won't be feasible at this rate. </div>
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<br>
</div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0); background-color: rgb(255, 255, 255);">
Is there some way to avoid this non-linear increase in time or would it be best to just write some python code to loop through smaller chunks of data and write the results somewhere?</div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0); background-color: rgb(255, 255, 255);">
<br>
</div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0); background-color: rgb(255, 255, 255);">
Regards,</div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0); background-color: rgb(255, 255, 255);">
Rory</div>
<br>
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