Lines and angles

[drlarrye]

I'm trying to make a dissection puzzle (take it apart and rebuild in a different shape) and I have a couple questions.

Is there a way to directly measure an angle or can you only measure it from the vertical or horizontal axis?

Referring to the attached drawing, how can I draw a line from the circled node to the line indicated by the arrow such that the drawn line will make a 90 degree angle with the existing line?


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[brynn]

Inkscape has a still relatively new feature, Snap Perpendicular, which sounds like it should be helpful.  However, I can't seem to figure out how to use it.  (I know how to enable it in Document Properties.  But I don't see how to set one line perpendicular to another.)

Just to be clear, you don't know exactly where the new path will meet the line which the arrow is pointing to, at 90°.  Right?  But you know it needs to start at a particular node on the other line.

Well, maybe someone else knows how to use that snap feature.  But meanwhile, I think this is how I would do it.

1 - duplicate the line with the arrow pointing to it
2 - move it away (just for clarity, but not absolutely necessary)
3 - with Selection tool, click a 2nd time on it, to reveal the rotation center and rotation arrows
4 - grab the rotation center and drag it towards one end of the path, and snap it to the end (let me know if you need help setting up snapping)
5 - drag it back over to where it came from, and snap the end with the rotation center to the original line - just snap it anywhere for now
6 - It's a little tricky to do this without using Object menu > Transform > Rotate, but it's possible.  As you rotate, watch the status bar and you can see the degrees.  Then just stop at 90°.  But if that's too tedious, you can use the Transform dialog, Rotate tab, and set for 90°, then click Apply.
7 - Now the line is at the proper angle.  So now you can snap the other end of it to the appropriate node, and it will intersect the original line at 90°
8 - However, the line is too long.  Using the Selection tool, grab the corner arrow at the top-left, hold the Ctrl key down, and drag it shorter.  If you have Snap to Paths button enabled on the snap control bar, the end should snap to that path.

I could make a video if that would be easier for you.

Is it going to be a tangram?

[drlarrye]

Perpendicular snapping worked well for me.  I had "snap to a line" on and turned on "snap perpendicular" in the document properties.  I wish there was an easier way to set angles as some of the other puzzles I would like to do have different angles.  I can trace them from a picture but I would like to be able to make them rather than just copy them.  I really like Inkscape, but I think I try to use it for things it wasn't actually designed for.

This particular puzzle only has 4 pieces, so it is easier.  It also makes a square.

Thanks

[drlarrye]

Next question...In the above project, I now have a line ending on another line (perpendicularly) and now I want to make a node on the original line in the same spot.  I know I can't attach the 2 lines the way I have them because there would be 3 attachments to a node, but I would like to have a node (in the middle of the line being attached to) in the same spot as the end node.

[brynn]

Perpendicular snapping worked well for me.  I had "snap to a line" on and turned on "snap perpendicular" in the document properties.  I wish there was an easier way to set angles as some of the other puzzles I would like to do have different angles.

1 - How did you get snap perpendicular to work?  I mean, after you enabled the proper settings, what did you drag and to where, how?  Is there some rotation involved?

2 - You can use the steps I provided, to achieve different angles.  Oh!  I just thought of maybe a better way....  This might be better, or it might just be another way.  Not sure.

 - drag out a guide and snap it to one end of the original line (the one with arrow pointing to it)
 - rotate it around and snap to the other end of that line
 - note the angle of that guide either in the status bar when your mouse is over top of the guide, or double-click on the guide to see the angle
 - add or subtract 90 to that angle
 - set up another guide at the new angle
 - snap that guide to the known node on the other line
 - now using the Pen tool, you can draw the new line, using snapping to intersection

I think I'd prefer this way to my original idea!

Your next question.  You want to put a node on the original line, at the 90° intersection.  There is a way to do that with snapping (snap to path intersection on snap control bar), but it's pretty tricky.  I think a video would be better for this, so I'll be right back.

[brynn]

Ok, here we go.  I used a similar setup as your first question. 

The special trick for this to work, is:

 - the line where you want to put the node is selected
 - the mouse has to be over the other line, and near the intersection

If the mouse isn't on the other line, the node won't end up at the intersection (it will end up where the mouse is).  In case you didn't alreay know, it's a double-click to set the new node.

[drlarrye]

Everything above is working great for me and I am moving on to more complicated Tangrams.  I have been able to do the simple one above and the most common one, which is 7 pieces.  I am moving on to one with curves which I should be able to figure out because the pattern is drawn with a grid.

My question is placing grid lines (or just regular lines that I could remove later) at specific intervals.  I have a 12cmx12cm square that I want to divide into thirds horizontally and vertically, ie. 9 internal squares.  Dividing it into halves/quarters/eighths etc is easy by placing nodes automatically but how can it be done at different but equal intervals?

[brynn]

As far as I can tell, by some simple testing I just did, Object menu > Align and Distribute should be able to do this. 

I just put the number of nodes that would be needed on the line.  So to make 9 cells, you would need 4 nodes - one on each end and 2 between.  Well, first, draw the line the length you need it, with one node on each end, of course.  The you can double-click on the path to add a node.  Do that twice.

Then get out Align and Distribute dialog.  When the Node tool is enabled, a different part of the dialog is displayed, than what you see with other tools.  I used Relative to:  Middle of section.  Then I clicked "Distribute selected nodes horizontally".  And it placed the nodes precisely where I expected.

Or, if the grid doesn't need to be permanent, and you won't be needing the lines of the grid for part of the drawing or path operations, you could use Inkscape's regular grids.  They aren't part of the drawing, and don't show up in the drawing (like for example if you uploaded to the internet).  So you would not need to draw the grid yourself.

They are completely configurable to whatever you need.  See File menu > Document Properties > Grids.  Not only you can configure the default grid that you see there, but you can create any number of additional grids.

[drlarrye]

Both perfect and easy after you do it the first time.

Thanks