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I am currently trying to label lines that I draw in my Map (in my iOS app, but I guess it applies to all maps).

So what I currently am doing, I simplify my path so that I get rid of most small curves and then just draw my glyphs along that line. Currently that looks like this:

enter image description here

On some parts of the line that's already ok. If the line is quite straight and the corners aren't too spiky.

But in some parts you can just not read anything... So what are strategies to make that look nicer? Does anybody know an algorithm or a strategy on how to make my path look like the red line here:

enter image description here

I am happy about any ideas on how to improve my drawing :)

Georg
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  • What you need is a smoother [Bezier Curve](https://en.wikipedia.org/wiki/B%C3%A9zier_curve) created using points on the actual line as control points. Check the [Adding Curves to Your Path](https://developer.apple.com/library/content/documentation/2DDrawing/Conceptual/DrawingPrintingiOS/BezierPaths/BezierPaths.html#//apple_ref/doc/uid/TP40010156-CH11-SW23) section to see how this can be done in Core Graphics path drawing. – Swapnil Luktuke Jan 03 '17 at 10:01
  • I updated my drawings above with numbers... So i guess I'd also have to filter out parts, where the angle between two vectors is too small?!? To get rid of point 5, 7, and 9?? And I can then smoothen the rest, right? I found a way nice to do that here: http://merowing.info/2012/04/drawing-smooth-lines-with-cocos2d-ios-inspired-by-paper/ – Georg Jan 03 '17 at 10:44

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I do it, in my commercial map rendering system, by finding a portion of the line without sharp corners. There is no way to make the label look good if it turns corners of a right angle or greater. If there's no section long enough I abbreviate the label (e.g., Link Road becomes Link Rd), or split it on to two lines. If there's still nowhere to draw the label I don't draw it.

Another thing that's important is to adjust the spacing so that ascenders and descenders don't clash, so you need to look at the bounding box of each adjacent pair of letters as you draw the text and add small amounts of space as necessary.

I don't bother to smooth my lines, as you suggest with your red line. It really doesn't seem to matter, at least with street labelling.

Graham Asher
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