QGIS make lines with offsets of y and azimuth from source and target coordinates

Question

I'm very new with QGIS and currently stuck with such problem in my work. Maybe some one knows how to help me?

I have made two separate layers.

1. Database layer with sites and antennas, containing site center points and azimuths with antennas. So I have created symbols representing such antennas by creating an offset from y points by the size of the symbol in a direction of azimuth data. It looks like this:

   

2. I need to analyse traffic between these antennas, which has enormous amount of data, so in order to not overload the system with data I import some data of wanted object (a new layer in QGIS) containing traffic destination with latitudes of source antenna and target antenna coordinates. together with that I import the azimuth info of both points.

So I create the lines using the function:

It looks like that when I enable both layers on the map:

So where is the problem?

If you look at this lines I cannot see from which sectors to which sectors of another object the line goes to because they all are drown from the centres. How can I make some offsets in the direction of known azimuth in the source point and target point?

In another words:
have lines like this: point1xy....point2xy
I want:
point1xy+y offset (-10) in direction (azimuth1).....point2xy+y offset (-10) in direction (azimuth2)

Answer 1

You could forgo your latitude and longitude fields, making your tables lighter. Instead you could have a simple int field with your target fid.

Of course, my answer assumes working with projected data, as far as distances are concerned, where map units are meters.

Here's a quick mockup of the required table for the lines to work:

I added an fid column for clarity, but it is not needed nor used. It's only to be able to see what the feature ID is at a glance.

The geometry generator expression, using projected points from the source and target geometries:

make_line(
   project($geometry,100,azimuth($geometry,geometry(get_feature_by_id('Points',attribute('target_fid'))))),
   project(geometry(get_feature_by_id('Points',attribute('target_fid'))),100,azimuth(geometry(get_feature_by_id('Points',attribute('target_fid'))),$geometry))
)

To explain the different functions:

• project(point,distance,direction) makes a new point from a starting point's position at a set distance, in a set direction (in radians)
• azimuth(point1,point2) simply returns the azimuth between the points in radians
• $geometry returns the geometry of the current feature so any function using this as a parameter will use the current feature's position
• geometry(feature) will return the geometry of a specified feature, which can also be used in other functions
• get_feature_by_id(layer,feature id) simply returns a certain feature by using its ID, in a specified layer

Adding everything up, the expression:

• Finds the azimuth between the source and the target
• Uses that azimuth to project a new point from the source towards the target (the target feature is found using the target_id field) at a specified distance
• Repeats the two first steps but in reverse, from the target towards the source
• Makes a line between the two projected points

If you'd like the distance to always remain the same regardless of zoom level, it's only a matter of using variables in the expression. For example, if your symbol measures 10mm, replace the 100 in my expression by 10*@map_scale/1000. This will multiply the 10mm by the map's current scale denominator, then put it in meters. Of course, this only works if the data is projected to meters.

So now, even if you move a point, the symbology will update without even having to edit any field in your table. The distance between the line and its originating point will also always be 10mm on-screen/on-print.

Here's my result with additional directional arrow on the lines and more points: