I created a layer to visualize cable-laying and want to export the sum of the cable-lengths to an excel file when I'm done so i created an attribute for it.
How do I link an attribute to the auto-calculated $length?
I am using QGIS 3.0
I added an attribute with the open-field-calculator and was able to set the formula round($length,2) to get the length as an output.
Adding it through the layer-properties didn't save the formula and just set the length for already existing attributes. Now every new added attribute automatically gets a length-value.