Topic: Draw arc by length, radius, and delta

[dbeach]

Hi,

Does anyone have a Lisp. that creates an arc by length, radius, and Delta letting me choose the first point?

Thanks,
Devon

[Dinosaur]

I think you will need to specify two more pieces of information to get an accurate curve for survey purposes - either the initial tangent bearing or radius bearing and the direction (left or right) of the curve.

[Anonymous]

I have a plan in front of me and given a line:

N64(degrees)00'00" Length: 40.61'

Then curve 1:
Delta:90(degrees)
Radius: 40'
Length: 62.83'

Curve 2:
Delta: 44(degrees)
Radius: 58.21'
Length 44.70'

so on and so on....

[Dent Cermak]

what you have is called "nothing". It's all fine and good to have the radius, delta and arc length, but you can do NOTHING without the chord direction (bearing) and distance. what you are saying is "I have point number one and this spiffy curve data to get to Point Number 2, But i really DO NOT know where point number 2 is."
You can compute all of the curve data remaining(tangent, chord distance, etc.) with no real problem, but if you do not already have Points 2,3, etc. , well Dude, you're screwed.
If the "experts' tell you that you have all you need, ask them for the deflection angle to point 2. Their eyes will glaze over.  

[Mark]

If I don't see a chord bearing then I can only assume it's a tangent curve and go from there. Otherwise punt!

[Dent Cermak]

multiple tangent curves!! OOOOOHH!! He's SO screwed!!

[Mark]

multiple tangent curves!! OOOOOHH!! He's SO screwed!!

How so? I deal with multiple tangent curves all the time; as in subdivisions.

[Dent Cermak]

Because the odds of the next curve's tangent being 90 degrees off the last is so slim. In our S/D plats they have to back up the lot line curves with a noted interior angle.(chord to property sidelot line). They don't allow more than 2 tangent curves and even then you have show either bearings or the interior angle to assist. matter of fact, our new regs state that all lines will have a BEARING and distance. Makes life so much easier. And now they are letting us BEGIN at GPS points! way cool. We still must state Quarter Section, but if no corner has been set, or is in place we no longer have to traverse 2 miles to tie it all down. State Plane coordinates rule!!
The engineers tell me that if they have 2 curves like that, they now have to have a short tangent section between the curves. i don't know why, but it makes sense to me.

[Dinosaur]

I have had only limited luck producing the exact curve I need with the chord and choird bearing as well Dent.  Unless you start with an EXACT bearing to base everything from rather than connect two points and list it as most everyone tends to do, any interior bearings that are not offsets or perpendiculars to your original baseline will be ever so close but not perfect.  If I don't have both tangents to a curve established, I will construct it with a perpendicular radius from the last point, rotate it per the delta angle, draw the curve and then prodeed along the tangent of the curve.  If the both tangents have been established, I fillet the exact radius and let the line segments absorb any length error.  These are the only two methods I am sure will produce curves that are precisely tangent and eliminate minute gaps and overlaps in lines and arcs offset from them.

[sinc]

Does anyone have a Lisp. that creates an arc by length, radius, and Delta letting me choose the first point?

Since you're posting this question in the Land Lubber forum, I'm assuming you have Land Desktop...

Land Desktop has a slew of options for creating lines, curves, compound curves, line/curves from the ends of other lines/curves, etc.  Why do you need a lisp routine?

[Dent Cermak]

Because the LDD stuff is like "Start, End, Radius". He has the "start', he has the "radius' but he doesn't have the "end" info. it takes a minimum of 3 elements to do an atc or a curve. GHe's wanting to do it with only 2 elements. SOL Duse.

[LE]

Hi,

Does anyone have a Lisp. that creates an arc by length, radius, and Delta letting me choose the first point?

Thanks,
Devon

Have a look at this on progress.....

[Dinosaur]

Luis,
I can not tell from your options how it would work for subdivision layouts, but I can certainly see its value for recreating a lot like we have to do for staking house locations and for doing a mapcheck for closure.

[LE]

Luis,
I can not tell from your options how it would work for subdivision layouts,

Hi,

Do you have a sample drawing I can use?....

This utility has 18 method's to draw arcs.


Thanks.

[Dinosaur]

Luis,
HERE is a stripped down subdivision layout that I think contains some areas with curves that have been created incorrectly.  I posted some of my methodology used to keep these errors to a minimum earlier in this thread.  This was taken from a base sheet in Civil 3d, but I exported to a r2000 format.  You can ignore any warnings about proxy objects - all have been removed.
The house stakeouts I mentioned would be recreated with completely new linework drawn only with the course information from the recorded plat which in nearly all circumstances has some degree of rounding area in every course.  The difference from the starting point and ending point of this traverse provides the data needed for the mapcheck analysis.