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.

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Best regards, Esteban Sent with [ProtonMail](https://protonmail.com) Secure Email. ‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐ On 7 March 2018 10:10 AM, Jakob Erdmann <namdre.s...@googlemail.com> 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 <ee...@protonmail.com>: > >> 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@eclipse.org >> To change your delivery options, retrieve your password, or unsubscribe from >> this list, visit >> https://dev.eclipse.org/mailman/listinfo/sumo-user

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