Re: [sumo-user] Can you clarify how density is computed for lanes and ed

[eegea <eegea@xxxxxxxxxxxxxx>]

Hello Jakob,

thanks a lot, now it is more clear.

The problem is that I was assuming that sampledSecond is just the number of seconds there were vehicles on the lane, not the sum of the number of seconds of every vehicle on the lane. I was assuming that if your measure interval is, say 10 s, then sampledSeconds<=10 always.  Even though it is on the wiki, I think it is not clear enough.

Best regards,

Esteban

Sent with ProtonMail Secure Email.

‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐

On 7 March 2018 10:10 AM, Jakob Erdmann <namdre.sumo@xxxxxxxxxxxxxx> wrote:

Hello,

I admit the formula is a bit hard to read.

Consider an aggregation period of 1s. In that case each vehicle on the lane results in 1 sampled second so sampleSeconds gives the number of vehicles on the lane.

Since the length of the lane is in m we get the density #veh/m by dividing by myLaneLength.

To get #veh/km we multiply by 1000

For longer periods, if the number of vehicle on the lane stays constant, it should be obvious that the sampleSeconds is a multiple of the number and the period and the formula is correct as well.

If the number of vehicles changes during the aggregation period, the formula gives the appropriate average.

regards,

Jakob

2018-03-06 18:59 GMT+01:00 eegea <eegea@xxxxxxxxxxxxxx>:

According to the wiki (http://sumo.dlr.de/wiki/Simulation/Output/Lane-_or_Edge-based_Traffic_Measures)

density is given as "#veh/km"

However, looking at the source in MSMeanData_Net line 179 and 208 it is computed as

dev.writeAttr("density", sampleSeconds / STEPS2TIME(period) * (SUMOReal) 1000 / myLaneLength)

I cannot see why the above gives the number of vehicles per Km in the lane during the period. As far as I see, sampleSeconds is updated as expected

sampleSeconds += timeOnLane

so it seems to be what the wiki says "Number seconds vehicles were measured on the edge/lane".

It seems that we have the fraction of time the lane has been occupied multiplied by 1000  and divided by the lane length.

Is this an error or is this coming from some formula I do not know of?

_______________________________________________

sumo-user mailing list

sumo-user@xxxxxxxxxxx

To change your delivery options, retrieve your password, or unsubscribe from this list, visit

https://dev.eclipse.org/mailman/listinfo/sumo-user