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The problem is how to split segments or in other words how to insert new points into a polygon so that the segment where I created the new point is now two segments connected by said point. Every time I create a new point within a segment, the segment stays the same length as before and is not being split by the new point. (I don't know why the following snapshots have double columns on the left side but just ignore that. was not like this in the program). First I have the segment I want to split:

segment is dark red between two points.

Then I go to edit mode for the segment layer, click on the knot tool and select the segment:

location where the segment should be split.

I double-click on the segment where i want a new point. The "new place for the point" appears:

enter image description here.

I then go to pointlayer, activate the edit mode, click on "add new element" and create a new point near the segment:

new point is shown near the "x".

After I activate the snap-function and define the radius, I place the point on the "x" with the knot-tool:

point is now in the right place.

Now if I go on the info-pointer and click on the segment, the segment is still as one piece and is not split by the new point:

still one segment.

Why?

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1 Answer

Use the Split Features tool in Advanced Digitizing toolbar.

It seems like you just added new vertices. Adding vertices to lines does not split lines and it shouldn't. That's a different use case.

I didn't not understand your reason for the point layer. You might want to elaborate on that if it's important.

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Thank you. At first i tried to create new segments with QGIS (for which i wouldn't need a point layer) but that failed (see my other thread about "Why does “save” overwrite the “capture point” function?"). My second thought was to create points with UIDs where i need them and tell SQL to draw the segment from UID x to UID y. A vertices (if it is the red cross on a segment) is not selectable and does not have an ID. That is why i need a point layer. Hope you get what i mean :-) –  Tudor Feb 13 '13 at 15:04
    
@Tudor: Does the Split features tool solve your problem? –  underdark Feb 13 '13 at 15:47
    
Sorry for the late answer. It does only partially solve my problem. It does split the segment, but when i save the project i loose one part of the segment i just split. It just disappears and isn't there anymore. Don't know what i am doing wrong. –  Tudor Feb 15 '13 at 14:45
    
Does the segment get lost when you save the project or when you finish editing? What's the layer's data source? A Shapfile, PostGIS, ...? –  underdark Feb 15 '13 at 15:28
    
When i finish editing. I don't really know what the source for the layer data is. I didn't create it myself. –  Tudor Feb 18 '13 at 10:27
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