Magnitude/Position undefined

[eewoz]

I am in 2d sketch and want to make a rectangle with the top side replaced by an arc. I draw the figure by

1. Draw and dimension a rectangle. The lower left corner of the rectangle is at the origin.
2. Draw an arc from the top left corner to the top right corner.
3. Delete the top of the original rectangle.
3. Constrain the right side of the rectangle to be equal and parallel to the left side of the rectangle.
The three sides of the figure are now fully defined but the magnitude and position of the arc are undefined. (The arc is red and the three sides are black.)
If I measure the arc with the ruler tool it displays the length of the arc as well as the coordinates of the two end points. I am able to extrude the figure after I exit 2D sketch so it must not be a real problem, but why does Alibre say that the magnitude and position of the arc are undefined?

 

[HaroldL]

why does Alibre say that the magnitude and position of the arc are undefined?

Because they are.
You need to add a dimension to define the radius. If it is supposed to be tangent to the sides of the rectangle then you need to add Tangent constraints. Also make sure the end points of the arc are coincident to the end points of the lines of the rectangle.

Here's a link to some Sketch tutorials. They may be a bit dated but they should cover the basics.

 

[simonb65]

... or just dimension the radius (magnitude) of the arc AND dimension the centre point (position) ... ideally to the square.

 

[eewoz]

Thanks guys. Adding some dimensions did the trick. It's tricky business because I had to give the arc a center point and two end points in order to draw it. Yet the arc wasn't defined until I gave a dimension to the center point. A similar thing happened when I replaced the the top side of the rectangle with an arc. The right side of the rectangle became undefined until I gave it a dimension. The tutorials that Harold referenced are also helpful. Thanks again for helping me see the light. I really appreciate it.

Ed