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30 Views, 2 Replies

03-15-2000 06:16 AM

If you try to draw a fitted curve through 3 points which you know are on

a parabola, QC7 doesn't draw a parabola at all. Normally, if you define

"n" points you would expect the fitted curve to be a polynomial of the

(n-1)th degree...at least that is the mathematical definition. However,

QC7 treats fitted curves differently as it lets you jump anywhere on the

screen so that you can even cross the curve unto itself, this- in

disagreement with the analytical model. I am just wondering what

mathematical formulation these curves have internally. There also seems

to be no way of snapping to them, except at the endpoints. Sorry for the

repost but this question has remained yet unanswered. :-)

a parabola, QC7 doesn't draw a parabola at all. Normally, if you define

"n" points you would expect the fitted curve to be a polynomial of the

(n-1)th degree...at least that is the mathematical definition. However,

QC7 treats fitted curves differently as it lets you jump anywhere on the

screen so that you can even cross the curve unto itself, this- in

disagreement with the analytical model. I am just wondering what

mathematical formulation these curves have internally. There also seems

to be no way of snapping to them, except at the endpoints. Sorry for the

repost but this question has remained yet unanswered. :-)

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03-17-2000 08:13 AM in reply to:
*MonkeyJump

I don't know alot about this, but I HATE unanswered posts (like mine)

so here goes.

The command you're talking about you have to select 3 points, right?

Well, I would guess the three points on your parabola are the (1) the vertex

(is that what you call it?) then two points, one resting on either side,

opposite each other.

First the Quickcad command is trying to make a circle. Or part of a circle

(an arc)

so here's what I'd do to get a parabola( note: the author of this post would

like to tell all that he's not sure this will work, it's just a thought, but

a phrase to all that would critisize- post something then!).

First, get that vertex(?) point.

Then you need 2 points on ONE SIDE of the parabola.

Draw the fitted curve.

Then mirror the half parabola you just drew to get the full monty, er,

parabola.

About the snapping thing, try highlighting the item in question,

then right-click, go to convert- take it from there, might work, might not,

you are trying the intersect command, aren't you moneyjump?

Lemme know if all that helps,

Don Becker

MonkeyJump wrote in message

news:38CF9B36.9716A411@videotron.ca...

> If you try to draw a fitted curve through 3 points which you know are on

> a parabola, QC7 doesn't draw a parabola at all. Normally, if you define

> "n" points you would expect the fitted curve to be a polynomial of the

> (n-1)th degree...at least that is the mathematical definition. However,

> QC7 treats fitted curves differently as it lets you jump anywhere on the

> screen so that you can even cross the curve unto itself, this- in

> disagreement with the analytical model. I am just wondering what

> mathematical formulation these curves have internally. There also seems

> to be no way of snapping to them, except at the endpoints. Sorry for the

> repost but this question has remained yet unanswered. :-)

so here goes.

The command you're talking about you have to select 3 points, right?

Well, I would guess the three points on your parabola are the (1) the vertex

(is that what you call it?) then two points, one resting on either side,

opposite each other.

First the Quickcad command is trying to make a circle. Or part of a circle

(an arc)

so here's what I'd do to get a parabola( note: the author of this post would

like to tell all that he's not sure this will work, it's just a thought, but

a phrase to all that would critisize- post something then!).

First, get that vertex(?) point.

Then you need 2 points on ONE SIDE of the parabola.

Draw the fitted curve.

Then mirror the half parabola you just drew to get the full monty, er,

parabola.

About the snapping thing, try highlighting the item in question,

then right-click, go to convert- take it from there, might work, might not,

you are trying the intersect command, aren't you moneyjump?

Lemme know if all that helps,

Don Becker

MonkeyJump

news:38CF9B36.9716A411@videotron.ca...

> If you try to draw a fitted curve through 3 points which you know are on

> a parabola, QC7 doesn't draw a parabola at all. Normally, if you define

> "n" points you would expect the fitted curve to be a polynomial of the

> (n-1)th degree...at least that is the mathematical definition. However,

> QC7 treats fitted curves differently as it lets you jump anywhere on the

> screen so that you can even cross the curve unto itself, this- in

> disagreement with the analytical model. I am just wondering what

> mathematical formulation these curves have internally. There also seems

> to be no way of snapping to them, except at the endpoints. Sorry for the

> repost but this question has remained yet unanswered. :-)

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05-08-2001 08:03 AM in reply to:
*MonkeyJump

Danny, QuickCAD and AutoCAD use existing geometry, typically, to snap to

control points when creating a splined curve (AutoCAD) or a fitted curve

in QuickCAD. Unfortunately, QuickCAD doesn't offer parametric entry of

curve formulae. One popular program that does allow formula input to

generate a curve is Mathematica, that will then allow you to calculate

the area under the curve, for example.

To create the parabola from existing points in QuickCAD use the

Draw/Curve/Fitted with grid snap on (if the existing points coincide

with grid points). Use Nearest Snap if the points are off-grid.

As far as internal mathematical formulation, here is an example of a

parabola created in AutoCAD and LISTed to view the internal geometry

positions of the control points: (Note: QuickCAD does not display this

level of detail for curves properties.)

Command: li

LIST 1 found

SPLINE Layer: "0"

Space: Model space

Color: 7 (white) Linetype: "BYLAYER"

Handle = 93

Length: 15.60

Order: 4

Properties: Planar, Non-Rational, Non-Periodic

Parametric Range: Start 0.00

End 15.23

Number of control points: 5

Control Points: X = 1.00 , Y = 3.00 , Z =

0.00

X = 2.00 , Y = 6.50 , Z =

0.00

X = 4.00 , Y = 13.50 , Z =

0.00

X = 6.00 , Y = 6.50 , Z =

0.00

X = 7.00 , Y = 3.00 , Z =

0.00

Number of fit points: 3

User Data: Fit Points

X = 1.00 , Y = 3.00 , Z =

0.00

X = 4.00 , Y = 10.00 , Z =

0.00

X = 7.00 , Y = 3.00 , Z =

0.00

Fit point tolerance: 1.00E-10

MonkeyJump wrote:

> If you try to draw a fitted curve through 3 points which you know are

> on

> a parabola, QC7 doesn't draw a parabola at all. Normally, if you

> define

> "n" points you would expect the fitted curve to be a polynomial of the

>

> (n-1)th degree...at least that is the mathematical definition.

> However,

> QC7 treats fitted curves differently as it lets you jump anywhere on

> the

> screen so that you can even cross the curve unto itself, this- in

> disagreement with the analytical model. I am just wondering what

> mathematical formulation these curves have internally. There also

> seems

> to be no way of snapping to them, except at the endpoints. Sorry for

> the

> repost but this question has remained yet unanswered. :-)

--

Bob Felton

Autodesk Product Support, USA

WW Support & Services, Autodesk

Discussion Q&A: http://www.autodesk.com/discussion

control points when creating a splined curve (AutoCAD) or a fitted curve

in QuickCAD. Unfortunately, QuickCAD doesn't offer parametric entry of

curve formulae. One popular program that does allow formula input to

generate a curve is Mathematica, that will then allow you to calculate

the area under the curve, for example.

To create the parabola from existing points in QuickCAD use the

Draw/Curve/Fitted with grid snap on (if the existing points coincide

with grid points). Use Nearest Snap if the points are off-grid.

As far as internal mathematical formulation, here is an example of a

parabola created in AutoCAD and LISTed to view the internal geometry

positions of the control points: (Note: QuickCAD does not display this

level of detail for curves properties.)

Command: li

LIST 1 found

SPLINE Layer: "0"

Space: Model space

Color: 7 (white) Linetype: "BYLAYER"

Handle = 93

Length: 15.60

Order: 4

Properties: Planar, Non-Rational, Non-Periodic

Parametric Range: Start 0.00

End 15.23

Number of control points: 5

Control Points: X = 1.00 , Y = 3.00 , Z =

0.00

X = 2.00 , Y = 6.50 , Z =

0.00

X = 4.00 , Y = 13.50 , Z =

0.00

X = 6.00 , Y = 6.50 , Z =

0.00

X = 7.00 , Y = 3.00 , Z =

0.00

Number of fit points: 3

User Data: Fit Points

X = 1.00 , Y = 3.00 , Z =

0.00

X = 4.00 , Y = 10.00 , Z =

0.00

X = 7.00 , Y = 3.00 , Z =

0.00

Fit point tolerance: 1.00E-10

MonkeyJump wrote:

> If you try to draw a fitted curve through 3 points which you know are

> on

> a parabola, QC7 doesn't draw a parabola at all. Normally, if you

> define

> "n" points you would expect the fitted curve to be a polynomial of the

>

> (n-1)th degree...at least that is the mathematical definition.

> However,

> QC7 treats fitted curves differently as it lets you jump anywhere on

> the

> screen so that you can even cross the curve unto itself, this- in

> disagreement with the analytical model. I am just wondering what

> mathematical formulation these curves have internally. There also

> seems

> to be no way of snapping to them, except at the endpoints. Sorry for

> the

> repost but this question has remained yet unanswered. :-)

--

Bob Felton

Autodesk Product Support, USA

WW Support & Services, Autodesk

Discussion Q&A: http://www.autodesk.com/discussion

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