Uniting 2 curves that touch each other leaves "stray anchors"

[Eroica]

Hi,

 

Imagine the following scenario shown in this screenshot:

 

 

Basically, I have 3 separate curves that make up the following grid:

OOOOOOOO
X-------
XBBBBBBB

I want to join O and X by "uniting" them (i.e. selecting them both and clicking on the "Addition" icon in the toolbar). What I expect is to get a reverse L shape consisting of 6 anchors, i.e.:

MMMMMMMM
M-------
MBBBBBBB

However, what I get is the following:

 

 

There is this stray anchor (inside the red circle) that somehow breaks this merged shape. If I remove it, it looks like this:

 

 

I'm never able to join those 2 curves into one. I tried selecting anchors of both curves and clicking on "Close curve"/"Connect curve" (inside the Action bar), but they don't seem to have an effect.

 

I'm sure I misunderstand how curves and anchors work together, if you could help me here and point me towards some resources to better understand them, that would be greatly appreciated!

 

EDIT

 

I just noticed that at the encircled section, there are actually 2 anchors on top of each other (I just deleted them both when I selected them by dragging a selection rectangle around them). If I move one anchor away, I get this:

 

 

What would be the proper way to merge this two curves?

[Alfred]

Using the Node Tool, drag the top of shape X upwards so that it overlaps shape O. You will then have a single closed curve (a 'Curve' object) instead of a polycurve (a 'Curves' object) when you add the two shapes.

 

You'll always get a Curves object when you add non-overlapping shapes. In cases like this it isn't obvious because the two shapes are butted up against each other, but they still aren't actually overlapping.

[Eroica]

I see, thanks for your reply, so I'd have to "bump" shape X into shape O before adding them. Out of curiosity, is there any way of uniting the two curves found in my 4th screenshot?

 

What surprises me is that in another test file (in which I tried out the same scenario), the resulting reverse L shape has a stray anchor as well, but when I remove that one, it doesn't break the shape (it's just an additional anchor on one side of the L).

[Alfred]

I see, thanks for your reply, so I'd have to "bump" shape X into shape O before adding them.

 

Exactly. :)

 

Out of curiosity, is there any way of uniting the two curves found in my 4th screenshot?

 

What do you want the end result to look like, Eroica? For a shape with a straight left-hand edge, you just need to increase the height of the rectangle from two squares to three before you perform the 'Add' operation.

[Eroica]

I'm sorry if this sounds somehow dumb, but please look at this process which I did in another file to test that scenario:

 

Two shapes before joining them:

 

 

After joining them:

 

 

(Take note of the additional anchor on the left side.)

 

After deleting that anchor:

 

 

So for me it seems that the "merge" process sometimes creates two anchors on top of each other on the left side which "break" the resulting shape, and sometimes (like in the picture above) it only leaves an additional anchor that you can simply delete.

 

What I would like to know is if the "merging" leaves two curves (basically the 4th screenshot in my original post), is there a way to join these curves into one curve? And why does the merging sometimes leave two anchors, and sometimes only one?

[Alfred]

You won't automatically get a single curve when joining two non-overlapping closed curves, but you can break the curves at a couple of places and then join them together in various ways. The extra nodes (or not) are probably just the result of differences in alignment.

[Eroica]

[...] but you can break the curves at a couple of places and then join them together in various ways. [...]

 

OK, and with the risk of sounding really dumb, how exactly do I join the two curves then? I know that I can select an anchor and "Open" the curve which moves the red anchor (which I assume is the end anchor) around, but how exactly do I join two end anchors (of two curves) into one?

[R C-R]

The Join Curves action only works on a pair of open curves. Moreover, it always joins them at the two nodes closest to each other -- you can't choose which end nodes will be joined. One of the problems with this is if you break a closed curve with the Break Curve action (which really just splits a single selected node into two unconnected ones at the same x & y coordinates) both of those nodes will be exactly the same distance from the nearest end node on the other open curve!

 

I have not figured out which node the app joins with the other curve when this happens (it seems to be random), but the only way I know to get consistent results is to either move one of the nodes a bit or to break the curve at another node (adding it first if necessary) & then deleting the extra curve this creates.

 

In theory, if one of the end nodes of one of the curves is coincident with one of the other (for instance because you snapped it to that point), the Join Curves action should combine them into a single node, but that seems to happen only occasionally.

[JimmyJack]

Are you sure your boxes are well aligned?

 

This is what I get after a simple boolean add. Quite a clean result. A pleasant surprise after past troubles.

 

[Eroica]

@JimmyJack

I used the grid to align them, and if I check each corner nodes' coordinates, they are the same. The strange thing is that I get the same behavior as yours in a test file, but not always (e.g. like in my original post).

 

@R C-R

Thanks for your explanation! I tried to do the steps you described to join two curves, but I discovered another problem. Look at this scenario (I'll link a screenshot because it would be too large to display inline): https://dl.dropboxusercontent.com/u/951334/Bildschirmfoto%202016-12-05%20um%2010.33.01.png

 

There are two curves as two separate objects (as seen in the layers panel). No matter which nodes I select, I'm somehow not possible to join these curves into one. Pressing "Join curve" or "Close curve" just doesn't do anything.

 

Another strange thing: I tested it once in a test file, and somehow that time it worked to connect the nodes. However, whenever I join these curves into one object like this (look at the layers pane, now there's only one object): https://dl.dropboxusercontent.com/u/951334/Bildschirmfoto%202016-12-05%20um%2010.36.11.png

 

I was never able to successfully merge these two curves into one.

 

So my question would be: In the 2nd screenshot of this post, and in the 4th screenshot of my original post---how am I able to join these two curves into one?

 

I'm sorry if that sounds repetitive, but I'm just not able to get it to work ...

 

EDIT

Alright, I think I've found my issue: My curves have to be open (which I understand), but I was never really sure when they are indeed open. As it turns out, I just missed the fact that an open curve misses a blue line between two nodes. It's a subtle detail, but so far my tests have been successful whenever I considered it.

 

EDIT 2

Hm, not so fast, I guess. If I unite those two curves into one (e.g. the 2nd screenshot in this post), I'm not able to merge the two curves into one, despite them having an open end, and a missing segment. Anyone able to replicate that?

[R C-R]

Eroica, I can't be sure from your screenshots but it looks like at least one & possibly both of the triangular shaped objects are closed curves -- the paths that define them connects all three of their nodes. As I said, you can only join two open curves. So Join Curves won't do anything & Close Curve will do the wrong thing or nothing.

 

If you are unsure if they are open or closed, switch to the Outline view mode, either from the View > View Mode menu item or by clicking on the third View Mode icon in the toolbar. If you see two V-shaped objects, each composed of two lines, then you can be sure the curves are open paths. If you still see the three triangle shapes, then they may be closed curves or they may be open ones with four nodes, two of which are on top of each other. To test for that, select one of the triangles with the node tool & click on (important!) & move its red node. If the path is open a gap will appear between that node & the one that was below it; otherwise the point of the triangle will move because there is just one node of a closed path there.

 

So if they are not open, to use the Join Curves action on these two shapes, you will need to open them before that will work. To do that, select any node (ideally the one nearest the other curve) & use the Break Curve action to separate it into two nodes. For clarity & tidiness you may also want to break another node on the same curve, the second nearest to the other curve, to create two separate curves & delete the one that is just a two node straight line. Do this for each of the triangle shapes that are not open.

 

Once you have two open curves, you can select them both & use the Join Curves action on them. You can then use the Close Curve action to close the curve if you want. You don't have to do that unless you want the triangles to have a stroked outline & for that stroke to go all the way around the shape.

 

What you have done in your second screen shot is to create a "Kurven" (note the plural) layer consisting of two unconnected paths, probably because you selected them both & used the Add boolean Operation one them. You can't join them unless you use the Divide boolean to separate them again & (if required) open their paths as above.

[Eroica]

@R C-R

THANK YOU very much for your thorough explanation! I think I'm slowly getting the hang of this process, and so far I could reproduce every scenario you described succesfully.

 

 

What you have done in your second screen shot is to create a "Kurven" (note the plural) layer consisting of two unconnected paths, probably because you selected them both & used the Add boolean Operation one them. You can't join them unless you use the Divide boolean to separate them again & (if required) open their paths as above.

 

That's exactly the case, and I would never had known that I first have to divide this "Kurven" object first to join the separate paths again! Thanks for your hint!