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Can you divide a curve using chord distances?

NickN

I have a plat with a cul-de-sac where I need to split the curve by the lot lines.

I drew in the cul-de-sac just fine, but the plat specifies that distances shown along curves (including cul-de-sacs) are chord lengths not arc lengths. I tried using units shortcuts in the divide tool but it doesn't seem to recognize them or I was doing it wrong. What's the proper way to do this or do I have to do the conversion to arc lengths myself?

Annotation 2022-03-15 160250.png

Thanks!

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anna_garrett

i've never seen that before and i'm sorry they did that! can you not just sketch the curve with the traverse tool using the chord direction & length parameters instead?

NickN

Since there's no curve table, just the chord lengths, I don't know the chord bearings of the individual lot frontages along the curve.

I can do the math to convert the chord lengths to arcs and then divide using those values but I just wanted to make sure I wasn't overlooking the proper way to do it.

anna_garrett

i genuinely can't think of a way to finagle the divide tool to fit the data you have.

i would just convert the values.

jcarlson

You probably can't do it with the Divide tool, but could you use the Split tool, then use the distance constraint to add your vertices? Still, very manual and tedious, though.

BillFox

you could draw in the lot lines (short them) and extend/intersect into your curve

BillFox

or, assume tangent curves and calculate your way around from the street bearing using deltas - similar to when they don't give you radial bearings.

NickN

Do you mean drawing the chords with the specified lengths where it intersects the curve then split at those?

jcarlson

Yes. When you're sketching the cutline in the Split tool, you can use all the same editing hotkeys and constraints as when you digitize new features.

So when you start drawing a cutline, you could add the first vertix at the beginning of the curve, then press D for "distance", enter the first chord length, add a vertex where that radius meets the curve.

Then just repeat for each chord! Your curve should split right at the vertices. The only problem with this method is that it will shift all of any potential error onto the final segment of the curve. Not perfect, but it works. If there's a significant error, it may be worth converting to arc lengths in order to divide everything proportionately.

AmirBar-Maor

ALL - I have updated this reply.

After further review by @TimHodson - this use of the the 'Distance' method and the 'Varying Distances' option + distribute proportionally will only work of all the chord length are equal. The reason for that is that the relationship between ArcLength and Chord length is NOT linear.

So using the previously proposed method will not work - back to the drawing board.

Previous reply:

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Use the Divide tool using the 'Distance' method and the 'Varying Distances' option.

Then use Chord distances but check the 'Distribute remaining length proportionally. It will split the geometry correctly but populate the chord distances as ArcLength distance. So you might want to run Update COGO after that. It might not work for everybody because Update COGO will set the COGO type to 'From Geometry' and might not get to the correct values if you don't have the Ground to Grid correction set properly.

jcarlson

Mind. Blown. This is an excellent approach.

NickN

Ah yeah, I had tried that and ended up with the situation you described where all the error is in the last segment. Looks like Amir's suggestion below is probably the way to go for this situation. Thanks for your input!

NickN

Perfect, that's what I ended up doing as the best/quickest "fabric" method. I just wasn't sure if I was missing some tool capability that would do the splits with chords. Thanks, Amir!

AmirBar-Maor

All - I have updated my reply above - it is NOT the solution.

Using chord length and the proposed method will only work if the chord lengths are equal.

Back to the drawing board...
@NickN - maybe you want to submit an idea for the Divide tool to support the entry of chord lengths to split a true curve.

NickN

will do, thanks for the heads up!

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