Drawing transects using point layer as start point

Question

I'm very new to QGIS 3 and I have a problem. I got a point.shp indicating coastal transects long the world's coast set 500 m apart. I selected a subset projecting only the sandy transects along the Dutch coastline. From these points I know want to create a 5 km long transect inland 90° to the existing shoreline. The first picture shows the available points, second picture is a zoom-in and the red lines indicate what I want to achieve. Is there any way on how to create these inland transects perpendicular to the shore? Any suggestions, insights, tips, etc?

Answer 1

It can be done using Geometry by expression tool (in Processing Toolbox > Vector geometry).

Assumption: (Please modify them as necessary)

• Your Dutch coastline layername: Coast
• The coastline layer has an id (e.g."fid") field, and the said coastline's id is 1 .

After starting Geometry by expression tool, please set parameters as:

• Input layer: your start points layer
• Output geometry: Line

(Geometry expression)

make_line($geometry, 
          project($geometry, 
                  5000, 
                  azimuth($geometry, 
                          closest_point(
                            geometry(get_feature('Coast','fid', '1')), 
                            $geometry))))

This expression may look complicated, but -

1. First, closest_point(geometry(get_feature('Coast','fid', '1')), $geometry) finds a point on the coastline which is at the shortest distance from your start points.
2. Then azimuth() will find the bearing of the above point from the start point.
3. And project($geometry, 5000, xxx) will move your start point to the azimuth() direction by 5000m.
4. Finally, make_line($geometry, xxxx) will draw a line from the start point to the project(ed) point in the above Step 3.

Answer 2

Firstly, thank you so much for taking the time to consider my issue. I tried to run the code you sent me. It works in the sense that it executes the command and I create an output .shp, however, it just projects an empty layer, despite the fact that I have an attribute table with information in it. Any suggestions on what goes wrong?

Answer 3

Thank you for baring with me. So, as you can see in the picture, I used the transect points layer as the input layer. All my layers are on the CSR Amersfoort / RD New 28992 However, my coastline does not only have one field, like in your example but a very extensive attribute table (see picture 2). Could this be the problem? If you, where did you get your Dutch coastline .shp file form? Maybe if I use your coastline layer it would work?