MATSim

[pandanwaffles]

Hi all,

I would like to enquire on some confusion I faced when doing the MATSim tutorial from the Noisemodelling documentation.

1. What is the reason to Create the 0dB Source table in step 5?

2. In step 6: Calculate Noise Maps, why are the noise level in the LDAY_GEOM negative values?
   

Below is the LDEN_GEOM I generated for my MATSim scenario

The output I got from RESULT_GEOM was in negative values as well. Is this right? If so, how should I visualise this on QGIS to make it non negative?

Would really appreciate your help and answer! Thank you!

Best regards,

[Nitnelav]

Hi, yes so,

With MATSIM, you get traffic conditions (LV, LV_SPD,...) every 15min or 60min. To avoid computing the propagation for each traffic condition, we compute the attenuation between sources (roads) and receivers before applying it to every traffic condition.

The attenuation is computed by setting all roads Lw to 0dB (this is the SOURCE_0DB table) and running the Noise_Level_From_Source script with the confExportSourceId parameter.

The result (LDAY_GEOM table) then has all negative values as it represents the Lp-Lw attenuation between every source-receiver.

Then to get the Lp for a specific traffic condition, we just have to arithmetically add the roads Lw in the LDAY_GEOM table and sum the contributing sources for every receiver.

Does it answer your question ?

[Nitnelav]

In RESULT_GEOM, assuming nothing went wrong, having negative values means :

• there is no traffic on the roads arround the receiver at the given timestamp (it often happens at night when there is very little traffic)
• there is no roads close enough to the receiver (not close enough = not in the propagation radius = no source-receiver attenuation exists in LDAY_GEOM)

Can you share details on your project ? Are you just trying to reproduce the example or are you using another Matsim simulation ?

[Nitnelav]

Can you look into your MATSIM_ROADS_STATS and MATSIM_ROADS_TRAFFIC tables ? Is there any traffic at all ?

[pandanwaffles]

Hi! Thank you for your reply once again!
I'm just working on a school project and experimenting with MATSim and Noisemodelling. Hence, I created a small MATSim scenario with less than 5 inputs.
Thank you for the details I have checked the 2 tables and I think I found the issue here but do correct me if my assumption is incorrect!

As my MATSim simulation was based on a really small scenario hence the traffic data was little.

Based on MATSIM_ROADS_STATS table only 2 traffic stats measurements

& MATSIM_ROADS table only 3 traffic recorded

Resulting in only 4 noise measurements in RESULTS_GEOM and the rest would be negative values.

Would my understanding/assumption be right? Thank you so much for clearing my doubt!

Best regards,

[Nitnelav]

Yep ! That looks coherent.
The rows in the MATSIM_ROADS do not correspond to "traffic recorded" but to "road segement" or "matsim link", the acutal traffic is in MATSIM_ROADS_TRAFFIC and the power levels are in MATSIM_ROADS_STATS. All are linked byt the LINK_ID field

[pandanwaffles]

I see, Noted with thanks!
Really appreciate the clarification and help! :)

Best regards,