Polyline arc direction

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aeg
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Polyline arc direction

Post by aeg » Sat Aug 29, 2015 6:56 am

Hi,

When drawing an arc in a polyline in QCAD 3.9.8, it seems that you can draw an arc that goes up and counterclockwise, or an arc that goes down and clockwise, but not one that goes down and counterclockwise or one that goes up and clockwise. For example, if you set radius=100 and sweep=180, you always get an arc that looks like ). Is there any way to get an arc that looks like U instead?

aeg
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Re: Polyline arc direction

Post by aeg » Sat Aug 29, 2015 7:06 am

To expand a bit... I want to draw a rectangle with radiused edges. With further experimentation, I found that it's possible to do this if I start at the upper-right corner of the rectangle, but not if I start at the lower-left corner.

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Husky
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Re: Polyline arc direction

Post by Husky » Sat Aug 29, 2015 8:16 am

Hi aeg - welcome to the forum!

The arc direction depends on the Mouse-pointer position. Move the mouse-pointer and you will see that the arc direction will follow the mouse.

Try it by yourself. :wink:
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aeg
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Re: Polyline arc direction

Post by aeg » Sat Aug 29, 2015 9:22 am

Hi Husky,

Thanks for your quick reply.

There are EIGHT possible ways to draw an arc, and by moving the mouse pointer I can choose from TWO of them. When drawing an arc as the first segment of a polyline, there is, as far as I can tell, no place anywhere on the screen I can put the mouse pointer that will yield an arc that goes down and counterclockwise.

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Husky
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Re: Polyline arc direction

Post by Husky » Sun Aug 30, 2015 1:04 am

Hi aeg,
aeg wrote:Hi,
When drawing an arc in a polyline in QCAD 3.9.8, ...
aeg wrote:Hi Husky,
There are EIGHT possible ways to draw an arc, and by moving the mouse pointer I can choose from TWO of them.
I assume that we are not talking about the same thing ...
... an arc on a polyline has only TWO possible direction - not eight.

If you are planing to draw a rectangle as a polyline you have to start the polyline with a straight line. Then you have to connect the 90° arc to get the rounded edge. This arc has only two possible directions.

Counter question: If you need a rectangle with rounded edges why you are not just create a rectangle and round the edges with the "Round" tool? Very easy task!

If you are still facing problems please tell as the tool chain you are using or post an example drawing. Thanks.
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aeg
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Re: Polyline arc direction

Post by aeg » Tue Sep 01, 2015 1:31 am

Hi Husky,
Husky wrote:I assume that we are not talking about the same thing ...
... an arc on a polyline has only TWO possible direction - not eight.

If you are planing to draw a rectangle as a polyline you have to start the polyline with a straight line. Then you have to connect the 90° arc to get the rounded edge. This arc has only two possible directions.
Yes, when drawing a rectangle with rounded edges, there are only two possible arc directions after a straight line, and QCAD allows both of these. If I start with a line, I can draw a rectangle with rounded edges, no matter what corner of the rectangle I start on. So, my original problem is solved.

However, QCAD also allows starting with an arc as the first vertex in the polyline - in which case, even for a rectangle, there are more than two geometrically permissible directions. QCAD only allows two.

As an aside, there are certain weird polylines that QCAD can represent but that apparently can't be entered with the polyline tool. For example, draw a plano-convex lens (flat top and bottom, one flat side, 180 degree outward curve for the other side). Then go into the property editor, find the vertex with bulge=1, and change it to -1. Now you have a plano-concave lens. Other such polylines include revclouds and the schematic symbol for a transformer winding.
Counter question: If you need a rectangle with rounded edges why you are not just create a rectangle and round the edges with the "Round" tool? Very easy task!
That works too, thanks.

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Husky
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Re: Polyline arc direction

Post by Husky » Tue Sep 01, 2015 8:43 am

Hi aeg,
aeg wrote:As an aside, there are certain weird polylines that QCAD can represent but that apparently can't be entered with the polyline tool
You should check out the QCAD Pro Version. There is a tool which creates polylines from segments (Line, Arc etc). In combine with splines, ellipse arcs etc - which have to be exploded to become a polyline - I can't imagine any shape you can't build with QCAD. And it is fast too!
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