Use the Align Nodes command to reposition nodes to lie on a straight line. You must first select the two nodes that define the straight line (alignment edge), and then select the nodes to move.
To access this panel, click 
().
In the Input parameters section of the dialog, select two nodes to identify a line onto which other selected nodes are to be aligned. Then select the nodes you would like to align.
In the Selection option section of the dialog, indicate whether you would like to use filtering and if so, the type of filtering.
Dialog elements
- Alignment node 1/2
- The Alignment node boxes are used to identify a line onto which other selected nodes are to be aligned.
Click on a node in the graphics window and its number will be displayed in the input box. After specifying the alignment edge, select the nodes to move.
Tip: The node layer must be turned on before using this feature. - Nodes to move
- Identifies the nodes that are to be aligned on the line you have identified in the two Alignment Node boxes.
Click on one or more nodes (remember to hold the Ctrl key down to select multiple nodes) in the graphics window and their number will be displayed in this input box, and click Apply.
Tip: The node layer must be turned on before using this feature.