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Spirals >180 Deg Deflection Angle

6 REPLIES 6
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Message 1 of 7
Anonymous
432 Views, 6 Replies

Spirals >180 Deg Deflection Angle

Quick question for those of you who use (or have used) alignment spirals in
real world applications.

As you may know, Land Desktop does not allow creation of a spiral with a
total deflection angle greater than 180 degrees. There is a mathematical
reason for this.

Question - Has anyone run into any specific cases where they needed a spiral
with a total deflection angle greater than 180 degrees? If you have, some
more detail would be helpful.

Thank you,
Mike

Autodesk, Inc.
Michael C. Rogerson, PE
Product Designer - Program Manager
ISD Civil Engineering Software Development
6 REPLIES 6
Message 2 of 7
Anonymous
in reply to: Anonymous

Is this not similar to having a triangle with more than 180 degrees total in
the 3 interior angles?


"Michael Rogerson" wrote in message
news:156AE291D93BBE54FA314ED5E220ED1F@in.WebX.maYIadrTaRb...
| Quick question for those of you who use (or have used) alignment spirals
in
| real world applications.
|
| As you may know, Land Desktop does not allow creation of a spiral with a
| total deflection angle greater than 180 degrees. There is a mathematical
| reason for this.
|
| Question - Has anyone run into any specific cases where they needed a
spiral
| with a total deflection angle greater than 180 degrees? If you have, some
| more detail would be helpful.
|
| Thank you,
| Mike
|
| Autodesk, Inc.
| Michael C. Rogerson, PE
| Product Designer - Program Manager
| ISD Civil Engineering Software Development
|
|
|
Message 3 of 7
Anonymous
in reply to: Anonymous

Hi Mike,

Bearing in mind that a driver has to assess the speed at which they can
drive around a curve and to do this they need to be able to see the curve,
it would seem fairly frightening to design a spiral through 90 degrees let
alone 180 degrees.

--


Laurie Comerford
CADApps
www.cadapps.com.au


"wfb" wrote in message
news:3A908D28A84BCD1D7495613993CC077B@in.WebX.maYIadrTaRb...
> Is this not similar to having a triangle with more than 180 degrees total
in
> the 3 interior angles?
>
>
> "Michael Rogerson" wrote in
message
> news:156AE291D93BBE54FA314ED5E220ED1F@in.WebX.maYIadrTaRb...
> | Quick question for those of you who use (or have used) alignment spirals
> in
> | real world applications.
> |
> | As you may know, Land Desktop does not allow creation of a spiral with a
> | total deflection angle greater than 180 degrees. There is a
mathematical
> | reason for this.
> |
> | Question - Has anyone run into any specific cases where they needed a
> spiral
> | with a total deflection angle greater than 180 degrees? If you have,
some
> | more detail would be helpful.
> |
> | Thank you,
> | Mike
> |
> | Autodesk, Inc.
> | Michael C. Rogerson, PE
> | Product Designer - Program Manager
> | ISD Civil Engineering Software Development
> |
> |
> |
>
>
Message 4 of 7
Anonymous
in reply to: Anonymous

Hi Laurie,
Agreed, frightening indeed! Not in roads typically but I have in pratice,
use a spiral lead-off line on a Runway/Taxiway intersection that was indeed
greater than 90 degrees, but not by much.

I'm thinking more along the lines of complex interchanges, cloverleaves,
snaking viaducts and the sort - if anyone has been held back by this
limitation.

regards,
Mike

"Laurie Comerford" wrote in message
news:37D85D08B8B752274F024B54817BCACD@in.WebX.maYIadrTaRb...
> Hi Mike,
>
> Bearing in mind that a driver has to assess the speed at which they can
> drive around a curve and to do this they need to be able to see the curve,
> it would seem fairly frightening to design a spiral through 90 degrees let
> alone 180 degrees.
>
> --
>
>
> Laurie Comerford
> CADApps
> www.cadapps.com.au
>
>
> "wfb" wrote in message
> news:3A908D28A84BCD1D7495613993CC077B@in.WebX.maYIadrTaRb...
> > Is this not similar to having a triangle with more than 180 degrees
total
> in
> > the 3 interior angles?
> >
> >
> > "Michael Rogerson" wrote in
> message
> > news:156AE291D93BBE54FA314ED5E220ED1F@in.WebX.maYIadrTaRb...
> > | Quick question for those of you who use (or have used) alignment
spirals
> > in
> > | real world applications.
> > |
> > | As you may know, Land Desktop does not allow creation of a spiral with
a
> > | total deflection angle greater than 180 degrees. There is a
> mathematical
> > | reason for this.
> > |
> > | Question - Has anyone run into any specific cases where they needed a
> > spiral
> > | with a total deflection angle greater than 180 degrees? If you have,
> some
> > | more detail would be helpful.
> > |
> > | Thank you,
> > | Mike
> > |
> > | Autodesk, Inc.
> > | Michael C. Rogerson, PE
> > | Product Designer - Program Manager
> > | ISD Civil Engineering Software Development
> > |
> > |
> > |
> >
> >
>
>
Message 5 of 7
Anonymous
in reply to: Anonymous

Couldn't a spiral for, say, a parking garage ramp or on/off ramp be > 180
degrees? (or the pedestrian ramps at Giants Stadium). I've often heard
these refered to as "spirals" but most likely because of their 3D shape, not
because they're spirals mathematically. I can't imagine any other time you
would use anything more than a very slight spiral. They are, after all,
just for transitions, and not the curve itself. I've only ever used
circular curves in roadway design, but that's just me. I have used spirals
in rail design, but they definately don't come close to 180 degrees.

Jon Rizzo
Langan Engineering and Environmental Services, Inc.




"Laurie Comerford" wrote in message
news:37D85D08B8B752274F024B54817BCACD@in.WebX.maYIadrTaRb...
> Hi Mike,
>
> Bearing in mind that a driver has to assess the speed at which they can
> drive around a curve and to do this they need to be able to see the curve,
> it would seem fairly frightening to design a spiral through 90 degrees let
> alone 180 degrees.
>
> --
>
>
> Laurie Comerford
> CADApps
> www.cadapps.com.au
>
>
> "wfb" wrote in message
> news:3A908D28A84BCD1D7495613993CC077B@in.WebX.maYIadrTaRb...
> > Is this not similar to having a triangle with more than 180 degrees
total
> in
> > the 3 interior angles?
> >
> >
> > "Michael Rogerson" wrote in
> message
> > news:156AE291D93BBE54FA314ED5E220ED1F@in.WebX.maYIadrTaRb...
> > | Quick question for those of you who use (or have used) alignment
spirals
> > in
> > | real world applications.
> > |
> > | As you may know, Land Desktop does not allow creation of a spiral with
a
> > | total deflection angle greater than 180 degrees. There is a
> mathematical
> > | reason for this.
> > |
> > | Question - Has anyone run into any specific cases where they needed a
> > spiral
> > | with a total deflection angle greater than 180 degrees? If you have,
> some
> > | more detail would be helpful.
> > |
> > | Thank you,
> > | Mike
> > |
> > | Autodesk, Inc.
> > | Michael C. Rogerson, PE
> > | Product Designer - Program Manager
> > | ISD Civil Engineering Software Development
> > |
> > |
> > |
> >
> >
>
>
Message 6 of 7
Anonymous
in reply to: Anonymous

Hi Mike,

My experience of airports is confined to inside an aluminium tube.

However, for intersections such as you describe, I can't see any difference
in principle. A constantly changing radius on a clover leaf where you
inevitably have grade changes as well seems just as frightening.

Lastly, as wfb indicated assuming a symmetrical curve, it you have an entry
spiral > 180 degrees, add an exit spiral > 180 degrees and you have gone
through > 360 degrees. I don't think I'd approve that sort of layout. Even
with a circular curve, you would have to wonder if there is a better
solution to the intersection layout.

--


Laurie Comerford
CADApps
www.cadapps.com.au


"Michael Rogerson" wrote in message
news:D6F1B79B06B9F5AB0FC95C4AF0C70053@in.WebX.maYIadrTaRb...
> Hi Laurie,
> Agreed, frightening indeed! Not in roads typically but I have in pratice,
> use a spiral lead-off line on a Runway/Taxiway intersection that was
indeed
> greater than 90 degrees, but not by much.
>
> I'm thinking more along the lines of complex interchanges, cloverleaves,
> snaking viaducts and the sort - if anyone has been held back by this
> limitation.
>
> regards,
> Mike
>
> "Laurie Comerford" wrote in message
> news:37D85D08B8B752274F024B54817BCACD@in.WebX.maYIadrTaRb...
> > Hi Mike,
> >
> > Bearing in mind that a driver has to assess the speed at which they can
> > drive around a curve and to do this they need to be able to see the
curve,
> > it would seem fairly frightening to design a spiral through 90 degrees
let
> > alone 180 degrees.
> >
> > --
> >
> >
> > Laurie Comerford
> > CADApps
> > www.cadapps.com.au
> >
> >
> > "wfb" wrote in message
> > news:3A908D28A84BCD1D7495613993CC077B@in.WebX.maYIadrTaRb...
> > > Is this not similar to having a triangle with more than 180 degrees
> total
> > in
> > > the 3 interior angles?
> > >
> > >
> > > "Michael Rogerson" wrote in
> > message
> > > news:156AE291D93BBE54FA314ED5E220ED1F@in.WebX.maYIadrTaRb...
> > > | Quick question for those of you who use (or have used) alignment
> spirals
> > > in
> > > | real world applications.
> > > |
> > > | As you may know, Land Desktop does not allow creation of a spiral
with
> a
> > > | total deflection angle greater than 180 degrees. There is a
> > mathematical
> > > | reason for this.
> > > |
> > > | Question - Has anyone run into any specific cases where they needed
a
> > > spiral
> > > | with a total deflection angle greater than 180 degrees? If you
have,
> > some
> > > | more detail would be helpful.
> > > |
> > > | Thank you,
> > > | Mike
> > > |
> > > | Autodesk, Inc.
> > > | Michael C. Rogerson, PE
> > > | Product Designer - Program Manager
> > > | ISD Civil Engineering Software Development
> > > |
> > > |
> > > |
> > >
> > >
> >
> >
>
>
Message 7 of 7
Anonymous
in reply to: Anonymous

For the "spiral" ramp - I think, as you say, more of a "Helix" rather than
any type of 2D spiral. Would make an interesting 2D alignment indeed.

I'm certainly not expecting that anyone needs a spiral greater than 180
degrees, nor I have not ever heard of a request for one, but if there is
anyone out there that can't get something accomplished because of this, I'm
like to hear.

Mike


"Jon Rizzo" wrote in message
news:077BACE3E38C2B97B20238C5DED07020@in.WebX.maYIadrTaRb...
> Couldn't a spiral for, say, a parking garage ramp or on/off ramp be > 180
> degrees? (or the pedestrian ramps at Giants Stadium). I've often heard
> these refered to as "spirals" but most likely because of their 3D shape,
not
> because they're spirals mathematically. I can't imagine any other time
you
> would use anything more than a very slight spiral. They are, after all,
> just for transitions, and not the curve itself. I've only ever used
> circular curves in roadway design, but that's just me. I have used
spirals
> in rail design, but they definately don't come close to 180 degrees.
>
> Jon Rizzo
> Langan Engineering and Environmental Services, Inc.
>
>
>
>
> "Laurie Comerford" wrote in message
> news:37D85D08B8B752274F024B54817BCACD@in.WebX.maYIadrTaRb...
> > Hi Mike,
> >
> > Bearing in mind that a driver has to assess the speed at which they can
> > drive around a curve and to do this they need to be able to see the
curve,
> > it would seem fairly frightening to design a spiral through 90 degrees
let
> > alone 180 degrees.
> >
> > --
> >
> >
> > Laurie Comerford
> > CADApps
> > www.cadapps.com.au
> >
> >
> > "wfb" wrote in message
> > news:3A908D28A84BCD1D7495613993CC077B@in.WebX.maYIadrTaRb...
> > > Is this not similar to having a triangle with more than 180 degrees
> total
> > in
> > > the 3 interior angles?
> > >
> > >
> > > "Michael Rogerson" wrote in
> > message
> > > news:156AE291D93BBE54FA314ED5E220ED1F@in.WebX.maYIadrTaRb...
> > > | Quick question for those of you who use (or have used) alignment
> spirals
> > > in
> > > | real world applications.
> > > |
> > > | As you may know, Land Desktop does not allow creation of a spiral
with
> a
> > > | total deflection angle greater than 180 degrees. There is a
> > mathematical
> > > | reason for this.
> > > |
> > > | Question - Has anyone run into any specific cases where they needed
a
> > > spiral
> > > | with a total deflection angle greater than 180 degrees? If you
have,
> > some
> > > | more detail would be helpful.
> > > |
> > > | Thank you,
> > > | Mike
> > > |
> > > | Autodesk, Inc.
> > > | Michael C. Rogerson, PE
> > > | Product Designer - Program Manager
> > > | ISD Civil Engineering Software Development
> > > |
> > > |
> > > |
> > >
> > >
> >
> >
>
>

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