This topic provides a brief guide to the PEN3D's Onground function. Scroll down for detailed descriptions.
This feature is for CoRTN road traffic noise models.
In some cases the terrain file encompasses the road as well as the surroundings. In these circumstances it may be desirable to ignore the road elevation entered during the digitising process and use the ground model to specify the height of the road. In these circumstances check Onground.
One feature of un-checking Onground is that, optionally, the road height may be recalculated based on the underlaying terrain.
Onground Convert window
Generally speaking Onground has slower calculation times as the gradient of the road segment (or part road segment) has to be calculated from the DTM model.
The normal model, though faster, cannot reproduce the details of a high quality terrain model without very short road segments.
For normal modeling situations there doesn't appear to be significant variation in the calculated results for the two cases. Thus, setting up a model with a high quality ground model would be preferred. However, the accuracy on the normal model should be checked if calculation times seem excessive.