Offset QGIS label for vector field markers, rotate and anchor them so they are fixed regardless of scale

Question

Working in QGIS 3.34.3 Prizren and have a points layer visualized as 2 blue vector field marker arrows (visualized by angles called angle rbear & lbear respectively). The grey arrow is the 3rd VFM layer and its angle is based on a heading field. All angles are measured clockwise from north (0-359).

The direction of arrows is fine but I want the labels to appear at the end of each arrow (only right label is shown here). Labels represent a left count and right count value. I have 2 rule based labels like this for the left & right arrows ("Count" * ("Direction" = 'Right').

What I have tried:

• Offset from point > quadrant: no expression, just chose a quadrant. This is the closest thing to what I want but the offset distance is too small.

• Rotating the point based on heading (grey arrow), then offsetting the label (Offset X,Y) but it does not move on an angle, it just moves 50 units right
• Offset X,Y override: array( x($geometry) + "length" * cos("rbear"), y($geometry) + "length" * sin("rbear"))

I think a Case Else won't work for a quadrant override because I would have to write too many statements for all the angles between 0-359 and wouldn't be able to control the precise angle of the label, only the quadrant.

I'll be exporting as a leaflet map with QGIS2Web so maybe I configure the left/right labels there instead of QGIS?

Solution

Created a rule for left labels and rule for right labels. For each, used geometry generator and used a data defined rotation based on the heading (small arrow)

(```make_point( $x+(sin(radians( "rhead" ))* 0.0007), $y+(cos(radians( "rhead" )) * 0.0007)))

Follow up question

Labels are nearly complete, but they appear too close to the points when zoomed out, and too far from the points when zoomed in. I tried setting scale dependent visibilities and a scale range, but these don't affect how far the label appears from the point at different scales.

Any ideas on how to dynamically generate the label offset based on zoom scale so that they still appear near the arrows when zoomed in (example below) This is what I want to do

This is what is happening, labels appear too close to point when zoomed out

and too far from point when zoomed in

Update

Used expression to prevent label from "moving further/closer" to the arrows when zooming in & out:

with_variable('reference_scale', 1800,
    make_point(
      $x + (sin(radians("rhead")) * (0.0007 * @map_scale / @reference_scale)),
      $y + (cos(radians("rhead")) * (0.0007 * @map_scale / @reference_scale))
    )
)

Answer 1

Based on your setup i would think there is two options. Each one has advantages and disadvantages. If you use a symbol marker you can just set it and forget it. The downside is that it does not remove labels when zooming out, so it is not good for dynamic labels. Here is my setup for that:

The (in my opinion) better method is to use actual labels, this can be accomplished by setting the label point using a formula. I used the geometry generator to generate a point based on a set distance (this could be set from a field too) and the azimuth of the point. See screenshots for details.

I then defined the rotation from the field and you get the labels where you want them. you can apply this method to your project for each of your rule based labels etc. Here is the formula I used:

make_point(
$x+(sin(radians( "Azimuth" ))* 15),
$y+(cos(radians( "Azimuth" )) * 15)
)

See screenshot.