Defined/Constrained Sketch Elements Behavior

[bwalker145]

Simple question regarding sketch behavior:

In the simple example below, why is the left vertical member & bottom horizontal member showing as fully constrained? The bottom corner is located to the origin, but the length of the members is still undefined. The Fusion documentation explicitly states that both size and position must be completely defined to fully constrain the sketch.

When I add a length dimension to the left vertical line, the top horizontal line now shows as constrained as well, when it's length is still undefined.

[TheCADWhisperer]

Endpoint of the lines is underdefined.

Delete the blue lines(s).  What do you observe?

[bwalker145]

Agreed, the endpoints are undefined (i.e. length). After deleting the two blue members, the remaining lines still display as constrained.

Even a single line shows as constrained with only the X defined, and both Y & length undefined. My expectation would be for these lines to be displayed as unconstrained (blue).

[bwalker145]

Look at the example below, none of the members are fully defined. I alternated X & Y constraints.

I thought it might be an odd interaction with the horizontal/vertical constraints, but am seeing the same behavior on lines with those removed.

[g-andresen]

Hi,

1. please show symbols in browser

2. please share the file for reply

günther

[bwalker145]

1. The browser accurately shows the sketch as under-constrained

2. File attached

[jeff_strater · Accepted solution]

I think that there is a bit of a misunderstanding of the geometry items, and what it means to fully constrain them.  A "line" in the normal understanding is actually 3 separate objects in the Fusion sketch solver:

1. one "line" object - a line is considered to be the infinite representation of the line.  It consists of a direction and a through point, (which may or may not be one of the sketch line's endpoints).
2. two points.  The points are constrained to lie on the line, and are interpreted as the start and end points of the "line segment".  When drawing a line segment in Fusion's graphics system, only the portion in between the start and end is drawn.

So, to fully constrain a sketch containing one line, you need to constrain these 3 objects.

In this sketch, none of the 3 are fully constrained:

The line's direction is constrained, but not its location.  Neither point is constrained.  If I add a dimension to the origin:

now, the line is fully constrained (drawn in black).  But the whole sketch is not fully constrained, because the two endpoints are not constrained.

Next, I can add a dimension to the bottom point:

now, that bottom point is fully constrained, but the sketch itself is not

so, adding one more dimension (either the length of the line, or another dimension from the origin) will achieve this:

Hope this helps clear up things a bit

[bwalker145]

Thanks Jeff, appreciate the explanation, that definitely clears it up. I didn't realize that the line object was treated as a separate infinite entity from end points, and explains the interaction with the different X/Y & Horizontal/Vertical constraints.

[g-andresen]

Hi,

In the gray environment, the color of the dot give no indication of the properties of the vector.

günther

[bwalker145]

Interesting, I can replicate the same behavior. The only environment that shows the open vector point on mine is Photo Booth [edit: and Infinity Pool].