QGIS leader line at centre of line feature

Question

I am using leader lines for line labels of vector line. I need to connect leader line with the centre of chosen lines (to have anchor point dropdown at the centre of a lines). Leader lines are now connected with a (perhaps?) closest point of chosen line. At pictures below is seen that direction of leader line changes depending on position of label. I need always have leader line at the centre of line. Can it be done? enter image description here

Answer 1

Right now, placement of callout (leader) lines is limited. QGIS 3.20 (out now) will add support for new options to place callout lines:

#3 Next up #QGIS now allows exact, interactive positioning of callout lines using the "move labels/callouts" tool

For the moment, you could create callout lines with Geometry generator. This works only for labels that ware moved manually before, using Move a Label or Diagram so that an auxiliary storage for the position of the label is created.

Also be aware that for line-features, the centroid often is not on the line itself, so better use the mid-point of the line that you can create with line_interpolate_point($geometry,length ($geometry)/2).

Use this expression to create a callout to this point from your labels using Geomtry generator with this expression:

make_line (
    make_point ( 
        "auxiliary_storage_labeling_positionx",  
        "auxiliary_storage_labeling_positiony" 
    ),
    line_interpolate_point(  
        $geometry, 
        length ($geometry)/2
    )
)

Screenshot: blue = line feature; black = automatic callout/leader line; red: leader line created with geometry generator to the centroid; orange: leader line created with the expression from above: