Displaying water movement paths over grid in QGIS

Question

I have an external .csv file with "From" cell, "To" cell, X, Y coordinates for the "From" cell, X Y coordinates for "To" cell and flow rate for water going from "From" cell to "to" cell. I can import this file in QGIS using Layer -> add Layer -> Add delimited text layer.

Each cell discharges water to one of its eight neighboring cells. My grid size is 80 x 80.

I would like to display water movement direction with an arrow for each cell.

Is there a way to do this in QGIS?

I do not want to use QGIS to determine the flow direction for me.

Edit your question and add a sample of the csv file as text. You also need to add a code attempt or your question is probably going to get closed — BERA, Nov 07 '22 at 18:35

Matt · Answer 1 · 2022-11-07T19:21:54.883

Assuming your "FROM" and "TO" fields are formatted like 'x, y', You can use a "Geometry Generator" symbol layer with the following expression:

make_line(                              -- make a line of the FROM and TO points
    make_point(                         -- make a point of the FROM x, y coordinates
        string_to_array("FROM")[0],     -- make an array of the FROM x, y coordinates and get the first element (x)
        string_to_array("FROM")[1]      -- make an array of the FROM x, y coordinates and get the second element (y)
    ),
    make_point(
        string_to_array("TO")[0],       -- make an array of the TO x, y coordinates and get the first element (x)
        string_to_array("TO")[1]        -- make an array of the TO x, y coordinates and get the second element (y)
    )
)

To create a Geometry Generator symbol layer: