[QGIS-Developer] 3D View Interface Usability

[Jed Frechette]

Hi Martin,

I’m glad to hear my impressions weren’t too far off. I do think there
are benefits to the GE style controls, especially for users that are
already familiar with that software. Perhaps it makes sense to keep
those controls as a separate navigation mode in addition to a new mode
that is better suited to more complex tasks? Although I guess there’s
the risk of muddying the interface by not picking one clear consistent
set of controls and optimizing them.

It’s interesting that you mention multiple viewports, as that would
actually be fairly low on my wish list. This may be a personal
preference, but I don’t use multiple views very often in applications
where I have access to them. There are definitely certain tasks which
are easier with multiple views so they are nice to have, but if I had
to choose I’d much rather have a single viewport that is very
efficient than multiple viewports that are less fluid. That’s what
most of my suggestions below are geared toward; a single viewport
where an experienced user can almost instantly navigate to the exact
view they want, potentially edit/create some data, and within a few
seconds be moving on to the next part of the scene.

I’ll provide links to a couple examples and videos at the end of my
post, but since there is so little consistency between 3D apps I want
to provide some justification for what I think works rather than just
say “Make it like my favorite program.”

Regardless of the exact control scheme, I think the most important
observation to make when designing a 3D interface is that for any type
of interactive task the user is constantly switching between
navigating around the scene and using tools to perform actions, e.g.
identify, measure, digitize, etc.. Therefore, switching between those
two modes of interaction needs to be as quick and easy as possible.
Clicking toolbar icons to switch modes works but is probably the
slowest way to do it. Some applications try to overload the mouse
buttons so you can navigate and use tools at the same time, but I’ve
never used a system like that which I thought worked well. I think
it’s much better to make a clear distinction between navigate mode and
tool mode and make the user responsible for switching between them via
hotkey. That way your tools can make use of all 3 mouse buttons
independently of your navigation control scheme, which can also
utilize all 3 buttons.

Although various applications have made different choices about the
hotkey to use, to me the space bar is the obvious choice. The space
bar is the most used key when typing and the navigation hotkey will be
the most used key while navigating in 3D view so it should be the
space bar too. The navigate hotkey could be used as a toggle, e.g.
with a tool active tap the spacebar to switch to navigate mode then
tap it again when you want to go back to the tool. Alternatively, the
hotkey could be a modifier, e.g. hold down the spacebar to navigate
then release it to return to the tool. Both can work well, but I
prefer the modifier approach. A modifier removes the need for an
indicator, e.g. different cursors, for which mode you’re currently in
like you would need with a toggle. In addition a modifier can act as a
hint to stay in dynamic mode if your viewport is set up to improve
interactive performance by rendering different LODs based on whether
the camera is currently static or dynamically moving.

The specific navigation control scheme I would advocate for is:

Dolly along camera z-axis (Space + RMB or Scroll wheel)
==========================================
QGIS already behaves this way so no changes here. Usage of the scroll
wheel is also consistent between the 2D and 3D views so that’s good.

Track along camera x & y axes (Space + MMB, Space + Shift + RMB)
===================================
The middle mouse button is used for the same movement in the 2D view
so it would be good to stay consistent with that. The alternate
mapping, Space + Shift+ RMB, is for laptop users that only have 2
trackpad buttons. By tracking along the camera x & y axes instead of
GE style tracking navigation is much more intuitive in a fully 3D
world and you eliminate the orientation dependence I referred to in my
first post.

Tumble (Space + LMB)
=================
Tumbling in QGIS is already pretty good. The only change I would make
is to pivot around the cursor’s current position rather than the
center of the viewport. uclaros already suggested this in the tracker
[1] and it would make precise navigation much easier.

Roll around camera z-axis (Space + Ctrl + LMB)
===================================
This is really useful when you just want to level the camera relative
to the horizon.

Box zoom (Space + Ctrl + RMB)
========================
Good for zooming in to a specific region of the scene.

Other navigation controls could certainly be added, e.g. restricting
tumbling around additional axes, but I think the controls above cover
the majority of needs.

Two applications I think serve as good examples of what works well are
Houdini and PolyWorks. They have both been around for decades and even
though they serve very different types of users and are used in very
different ways their control schemes are remarkably similar. I used
their control schemes as the basis for the one I described above.
Houdini has good documentation, including lot’s of videos [2], and has
a free version so it is the easiest to observe in use. In contrast,
PolyWorks might cost you a kidney to evaluate. I do, however, have a
video I recorded a while ago showing it being used for some simple
feature extraction [3]. This is the kind of task I would love to be
able to do in QGIS. If I was designing a UI from the ground up for
that specific type of feature extraction it would be a little
different than what’s shown in the video, but it does give a good idea
of the type of fluid, highly interactive workflow, I’d be aiming for.

Hopefully, some of this is useful and provides some inspiration. I’m
afraid I’m not familiar enough with Qt to implement any of it myself,
but would love to be able to help in any other way that I can.

Best wishes,

[1] https://github.com/qgis/QGIS/issues/40530#issuecomment-742092974
[2] https://www.sidefx.com/docs/houdini/basics/view.html
[3] https://youtu.be/d5__-Vu6RkA?t=155


--
Jed Frechette