"Point not on entity" error - Alignment.StationOffsetByPoint Node

Dear all,

I have been using the “Alignment.StationOffsetByPoint” successfully, but for a few instances i encounter the “Point not on entity error”. Would you be able to advise as to why this error is issued and any workarounds? Also is it expected that such an error would be generated, when dealing with non-tangential alignments such as the ones created from CAD entities?

Basically i have 2 alignments and i would like to use chainage values from the parent alignment and project these onto an adjoining alignment to determine corresponding station and offset. I am using the “Alignment.StationOffsetByPoint” node and encounter the “Point not on entity” error which in turn returns nulls values for station and offset for particular chainages.

I have gone through this forum and found a python script by @Paolo_Emilio_Serra1 (attached) which triggers the same error for me of “Point not on Entity”. Any advise in this regard, would be much appreciated.

GetStationOffsetByNameEastingNorthing.dyn (10.6 KB)

Best regards

I’d have to see the DWG to know for sure, but it seems like you’re trying to get the station/offset of a point that is outside the bounds of the second alignment.

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Thanks again @mzjensen for your response, much appreciated.

I have attached the files in question and you will see that the C3D model contains 2 alignments and the dynamo script is attempting to use station values from the parent alignment to determine corresponding station value on the 2ND alignment. I have also purposefully setup the 2ND alignment as a non tangential alignment created through converting a CAD feature line into a C3D alignment, as i suspect this is contributing to the error.

The script throws the “Point not on entity” error at chainage 13180 to be precise and if you could advise if this is out of bounds then that would enable me to understand this aspect better. By the way would you know of the limit of these regions / boundaries that you have illustrated in your drawing?

Best regards

Alignment Offsets1.dwg (2.3 MB) Alignment Offsets1.dyn (20.7 KB)

Hmm, I am seeing the same thing. That is very interesting.

We can see if maybe @Paolo_Emilio_Serra1 has any thoughts?

I’m using an example to exaggerate what is happening here.
By definition, to determine the station of an object we need to project a point orthogonally on the alignment. In the picture below, said projection can be found for points A and C.
However for point B it is not possible to determine the station and for what it matters for any point that falls in the green area.

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If you replace the first station with this 13179.992664, you get the idea of how small is the error.
This happened because the second alignment is only made of lines with no curves in between.

Great explanation!