Time in Hotspot

Brett Lord-CastilloGIS ProgrammerSt Louis County Emergency Management

April 10th, 2013

A simple problem

Given a set of designated crime “Hotspots” Find out how much time police vehicles spend in those hotspots Which hotspots? Which days? What hours? Which cars?

The data

Automatic Vehicle Location (AVL) Car ID Latitude/Longitude Timestamp

Every 30 seconds per vehicle Hundreds of thousands of records per day

The data-complications

No specific order Transmitters malfunction (and we lose a car) Receiver malfunctions (and we lose hours) 5 minute stopped = stops transmitting

(But GPS Drift can bring it back on) Thirty seconds is rarely thirty seconds New dataset every day

(And sometimes we even lose a day)

Manual method

Convert Latitude/Longitude to XY Point table Select by Location with Hotspots polygons

Export and sum up number of returns Assume each return is 30 seconds

-or- Manually assign times to each point Sum up time on all returns

Why manual doesn’t work

Very time consuming, especially with manually assigned times

Have to redo selections for each dimension By Hotspot By Car By Day of Week By Time of Day

The Workspace

Not as complicated as it looks

Initialize and collect recordswith a blocking transformer

Inside the Loop: Three Date Formats

Day of the Week: String created by format %a (Name of day of week)Hour of Day: Number created by format %H (24-hour hour of day)epoch: Number created by format %s (seconds since epoch)_totaltime: Placeholder to assign time for each GPS return

Get some more information

fme_feature_type: Keep track of which points are from this week_prevcar: Car ID from the last feature processed

(We store this later)

Assign the time this return is worth

Set aside info for next feature

Spatial FilterSelect by Location, Spatial Join,and Blocking Transformer all in one

Output: Save Our Work(With fanout writer)

Week1019_1025 Pings1019_1025

Points for analysisAnd one sheet in an Excel Workbook

Last two sheets in the workbook

Outcomes

Comparison

First manual attempt took over 4 hours (To process one day) And assumed one point = 30 seconds Single stat (total time by hotspot)

FME ran entire week in under 30 minutes Automated Less assumptions More dimensions (By Car, By Day, By Hour)

Thank You!

Questions?

For more information: Brett Lord-Castillo, blord-castillo@stlouisco.com

St Louis County Emergency Management

@blordcastillo https://github.com/marigolds6