Constraining a spline?

øyvind_kaurstad

I recently tried creating a model where I imported an image of the model to trace over. The imported image was not centered over the origin (I sketched it on the top view). I traced the outline of the model (to later extrude), and for some parts I used splines.

Then I realized I wanted to align a specific feature in the sketch to the origin, but I just could not find a way. I added a single point to the model, and then tried to add a coincident constraint between this point and the origin. That would move most of my modeled features as intended, but not the splines, just the end points of the splines.

The whole thing was just a mess, so at some point I just gave up, and re-modeled using arcs instead of splines, and in the end I got where I wanted.
Is it necessary to constrain each and every point of a spline to something else to prevent this from happening?

joris_kofman

Each control point of a spline has the same degrees of freedom as a normal point would have. So if you want to move the whole thing you will have to establish relations between the geometry that tells the sketch how to move the points.

Else you should be able to use the pattern feature to create a copy of the sketch entries in the desired location.

joris_kofman

Each control point of a spline has the same degrees of freedom as a normal point would have. So if you want to move the whole thing you will have to establish relations between the geometry that tells the sketch how to move the points.

Else you should be able to use the pattern feature to create a copy of the sketch entries in the desired location.

joris_kofman

It would be great for this type of jobs if there was a "in relation to" constraint. But there alas is not

øyvind_kaurstad

Ok, thanks.
The need to explicitly constrain each and every spline control point greatly reduces the use of this line type, I think. The beauty of a spline is to easily draw more complex shapes, but typically you want the spline to act as a single unit afterwards, only constrained by the endpoints.

joris_kofman

i don't know of a single MCAD application that treats splines in the way you are outlining.

But what I think we do need is a tool that allows us to trace edges of images that are imported, and then constrain the points on the image.
This would allow one to import images that are not perfectly aligned and that have some arbitrary scaling factor. Then after tracing the lines that are needed one should be able to constrain everything to the image (even corners of other images) and input a single measured dimension (maybe one in each direction) and use a couple of aligning constraints to get everything square and neat with respect to the origin.

andrew_troup

joris_kofman said:

It would be great for this type of jobs if there was a "in relation to" constraint. But there alas is not

Do you mean, a bit like "Group" these entities, so they move together?
That would indeed be fantastic, particularly if kept really simple. (NOT like blocks in Solidworks: way too ambitious and arcane)
A sketch might automatically allocate numbers to each group, so that when you audit the constraints, you know which group a particular entity belongs to.

joris_kofman

@andrew_troup kind of like a group but I would like to be able to scale that group since sometimes you don't know what the scale of an image is, so you need to trace the outline, group the whole thing, rotate and move to get the axis right and then add a dimension that scales the whole thing.
Group would be a much better name for the feature than constrain in place, but key is the ability to scale the whole group as one.

andrew_troup

@joris_kofman
Ability to scale a group would indeed be very handy on occasions. And of course rotate and flip (not least, for nesting parts onto a sheet)