[Qgis-user] Node Tool - proposing improvements

[Bernhard Ströbl]

Dear all,

I want to apologize, this has become an extremely long mail...

A lot of discussion has been going on about the recent reimplementation 
of the node tool in QGIS 3.

I see two reasons for this:
1) The way the tool works is very different from the way it used to work 
in QGIS 2:
a) in QGIS 2 it was choose feature - choose node(s) - do something 
whereas in QGIS 3 it is choose node - do something
b) to move a node was click - (keep pressed) - move - release which was 
changed to click - release - move - click - release
2) There have been several bugs (as could be expected with a new 
implementation). These, however, were used to question the whole feature 
(most of the bugs are fixed now).

Apart from bugs and people not being used to the new tool the critics 
concentrate around:
1) Probably most annoying: Mouse movements for choosing an existing 
vertex/adding a new vertex at the middle of the line are not well 
defined (especially important if features and its vertices are very 
close together). Imagine a polygon surrounded (or even worse: 
overlapped) by others, now try to click a particular vertex. You will 
fail if always the neighbouring polygon is highlighted. The workaround 
is to select the vertex with a mouse window while its feature is 
highlighted (or previously select the feature e.g. with the 
Select-Feature tool). For overlapping features it is even harder.
2) Highlighting effect is disturbing.
3) Adding a new vertex puts the new vertex on the mouse ready to be 
moved but user has no intention to move it but to leave it where it has 
been added (e.g. for topological reasons).
4) Vertices are not visible all the time but only when the feature is 
highlighted. This can make choosing a particular vertex difficult (see 
also 1).
5) It is easy to accidentally add or move a vertex because the most 
intuitive way of selecting something is to click it. But when you click 
a vertex/segment/cross while being highlighted you are already on your 
way to move it.
6) The behaviour is not consistent:
a) If you want to move _one_ vertex, try to grab it when it is 
highlighted then move it; if you want to move several vertices, first 
select them, then click them, then move them.
b) If you want to delete a vertex, try to grab it when it is 
highlighted; if you want to delete a segment, do not try to grab it when 
it is highlighted but select its two vertices and delete them.

The German user group thinks that the points raised above are valid, 
even if all pending bugs are fixed. The node tool is still not perfect 
(it wasn't in QGIS 2 either).

So we propose a change in the way the node tool works and would like to 
hear other users' s opinions.
While the click - move - click change has valid reasons (use advance 
digitizing panel, pan or zoom map while moving vertices) the dropping of 
the first choose feature - then choose vertex workflow to immediately 
move a vertex has no real reasoning (except that it is less clicks in 
those cases where the node can be easily grabbed in the first place). 
But this new workflow is the main cause for the problems listed above.

Therefore we would like to see the old workflow reimplemented with some 
of the new ideas added plus some new ingredients. This is the draft for 
how the tool might work in the future:

1) While the mouse is moved around features are highlighted to indicate 
they can be edited. Furthermore eventual vertices, segments or crosses 
are highlighted, too (as in QGIS 3).
2) While a feature is being highlighted, it can be chosen with a left 
click (new).
3) If the user makes a right click instead, another (adjacent) feature 
is highlighted and can be chosen with a subsequent left click and so on 
(new).
4) As soon as a feature is chosen, the Vertex-Editor panel is opened (as 
in QGIS 2).
5) A chosen feature is the only feature whose vertices can be edited at 
that point* (as in QGIS 2). The chosen feature and all its vertices stay 
visible until the end of this feature's editing session (as in QGIS 2). 
If a vertex was highlighted it is immediately selected, if a segment was 
highlighted, its two vertices are immediately selected, if the middle of 
a segment was highlighted with a cross a new vertex is created there and 
immediately selected (new).
6) A vertex is selected by left clicking on it (as in QGIS 2).
7) Several vertices are selected by using a mouse window (as in QGIS 2 
and 3).
8) A click on a segment selects its two vertices (as in QGIS 2).
9) Vertices can be selected via the Vertex-Editor panel, too (as was in 
QGIS 2)
10) Every new vertex selection clears any previuos selection except if 
Crtl is pressed which adds the new selection to the current if vertices 
were not selected or subtracts them from the current selection if they 
were selected (as in QGIS 2).
11) Selected vertices can be deleted (as in QGIS 2 and 3).
12) Selected vertices can be moved by clicking either of them, thus the 
vertex (the vertices) are attached to the mouse and can be dropped with 
another left click (as in QGIS 3). A right click aborts the moving 
operation but the vertices are still selected (new).
13) A new vertex can be created by double clicking on any segment (as in 
QGIS 2 and 3), the new vertex is immediately selected (new).
14) A right click ends the chosen feature's editing session, if another 
feature is within reach it is immediately highlighted, continue as in 1) 
(new).
14b) To be discussed: Left clicking another feature immediately chooses 
this feature (as in QGIS 2).

* topological editing is still posssible, of course

We see the following advantages in this approach:
1) The new quick editing possibilities are preserved, there is just one 
additional click (compared to current QGIS 3) to move an existing vertex 
or segment or to create and immediately move a new vertex.
2) It is easier to create a new vertex in place.
3) It is a lot easier to graphically choose the feature to edit.
4) The highlighting indicates, which feature will be chosen by an 
immediate click, no surprises for the user.
5) It is easier to graphically select the vertices to edit.
6) The workflow is always the same: Choose feature - select vertices - 
do something with them.
7) The workflow is consistent with creating a new feature (right click 
to finish editing).
8) The application is more consistent because graphically selecting 
vertices works the exact same way as graphically selecting features with 
the Select-features tool.

I appreciate your feedback

Bernhard


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