Adding new vertex using QGIS Vertex editor

Question

I'm having trouble adding new vertex using the QGIS3 Vertex Editor - I'm using QGIS version 3.4.1-Madeira. I tried following the instructions provided in answer to Using QGIS vertex editor?.

The instructions stated:

QGIS 3.0 - Two options to add a new vertex:

1. Double-click on a segment to add a new vertex. The new vertex starts out selected and stuck to the cursor. Click a third time to place the vertex.

2. When hovering over a segment, there is an X in the middle of the segment. Click on the x to add a new vertex. The new vertex starts out selected and stuck to the cursor. Click a third time to place the vertex.

I've tried both of these with the following results:

1. double clicking on a segment seems to select and move an existing vertex,

and

2. hovering over a segment does not result in an x in the middle of the segment that I can click and move.

I have tried both options 1 and 2 above with snapping enabled and disabled and this doesn't seem to make any difference.

Any suggestions as to what I'm doing wrong?

Answer 1

To add a new vertex, hover the mouse over a line segment between two vertices. If your existing vertices are too close together, the vertex tool will tend to interact with the existing vertices instead of letting you create a new vertex.

Zoom in on the feature until the existing vertices are at least 1 cm apart. Once there's enough space between the vertices, the vertex tool can interact with the line segment instead of the existing vertices, and you should see a + sign when the mouse is over a line segment.

Answer 2

QGIS 3.4 on Windows 8 here. My use of the digitizing tool:

1. I first select the layer I want to edit and toggle editing

2. I select the current layer to make sure i am not editing unwanted layers (can happen if they are overlapping)

3. I hover over the polygon I want to edit. The corners of the polygon are now little circles. (I have also hidden the background image so you better see what is going on)

5. When clicking once on one of these vertex, I am able to move my mouse selecting the new position of this vertex. A second click will define the new location.

6. If instead of clicking on a vertex, I hover on top of the middle point of a segment, a small cross appears (visible on image 3). Clicking on it will allow you to add a vertex, and move it to the desired place.

1. Dont forget to save your edits!

Answer 3

Just as previous answer says, you need to zoom in enough to make QGIS to realize that you want to add new vertex, but not edit existing ones.

This is the key. How can QGIS know you are editing existing vertices? QGIS simplifies the task by the distance measured under the current project coordinate referencing system.

If you use crs like UTM/WebMercator, coordinate values are usually very large so it's very easy to distinguish vertices. However, if you use WGS84 or other things which limit the coordinate value into a small range, like [-180, +180] etc., then obviously the distance between 2 points will be very small. This makes QGIS believe you want to edit existing vertices.

So the solution is to change the project crs and use Mercator or UTM or anything else with large coordinate values instead.

Answer 4

If the red cross does not appear, it may be worth updating QGIS.

Here is the video how to do that.

I'm using keyboard shortcuts to switch between add polygon feature and vertex tools.

Answer 5

Caution. In some versions of QGIS it only works if you have the pixel option enabled instead of map units.