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In QGIS 2.12 the curves tool is integrated by default, I know. I would like to test the Spline Plugin whether it works better for my purpose or not (purpose is just to digitize streets mit nice curves, that's all).

The problem is, it doesn't work. There are the same edged lines as the standard drawing tool creates. I tried... ... to vary setting values. ... to reinstall the plugin. ... to use it in older versions (2.8 and 2.10). ... checking the option for ”suppress attribute form pop-up after feature creation” found in settings-options-digitizing-feature creation (as an answer to a similar question said).

None of this worked for me. Do I have to press a key while drawing or is there something else I can do?

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2 Answers 2

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This is 1 year too late, and my apologies for starting this with a question.

Do you happen to work on geographic coordinates (latitude-longitude) such as WGS84 ?

[This answer is assuming you are on Lat-Lon environment. Otherwise please wave this off...]

I suppose Spline Tool is a great tool, but it was probably designed for projected Xm-Ym coordinate system. It monitors X-Y distance between our mouse-clicks, and automatically calculate and update best fitting spline curves. It should work great if we move our mouse 50m to the next point, but it may mean somewhere around 0.0005 degrees (Lat-Lon-wise). Spline Tool cannot tell what happened.

To signal Spline Tool that our mouse has moved, we need to set the Tolerance to very small number, say 0.001 or even 0.000001, depending on the scale we are working on.

enter image description here

Unfortunately its user interface is not intuitive enough, as the Up/Down arrows changes only +1.0 or -1.0 incremental value...

You will see how Tolerance affects your result in the image below. spline curves with varied tolerance values

In this test, I tried to draw a polygonal line of 4 points on a map view at 1:25,000 scale (whatever it means) as shown in (1); starting from lower left, goeing up, then down, and backing up again to stop at upper right corner.

Then I activated Spline Tool, and applied various Tolerance values:

  • (2) Tolerance: 1.0
  • (3) Tolerance: 0.001
  • (4) Tolerance: 0.0001
  • (5) Tolerance: 0.00001
  • (6) Tolerance: 0.000001

You will see neither (2) 1.0 or (3) 0.001 do not show any effect at this scale. But it started to work at (4) 0.0001, and (5) 0.00001 looks fine to me. However (6) 0.000001 seems rather too busy.

Anyway you should be able to find best Tolerance value, fit for your task.

This test was made using QGIS 2.14.7 on Windows, but probably applicable to other versions (2.0 and after).

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  • The answer is a year late, too, but thank you. I did work on geo. coordinates, yes. I can't test it, but I guess this is the answer.
    – Grete Samsa
    Nov 15, 2017 at 13:32
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I think that's the way the plugin works, it creates curves but at a advanced zoom level you will see edges.

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  • It doesn't create curves no matter on what level I work. It doesn't matter if I work a scale 1:2500 or 1:250000. But thanks for answering.
    – Grete Samsa
    Nov 10, 2015 at 14:52
  • it works for me on Qgis 2.10.1
    – Youssef
    Nov 10, 2015 at 14:57

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