How do I place a component in the center of the board?

[malrip]

I'm attempting to align some components, such as an OLED display and a push-button, to the pcb board's centerline. The board was imported as STEP from Solidworks and has a non-uniform format (not a rectangle). The issue is that I've already completed the layout and origins from CAD to Altium  have been forgotten, making it nearly impossible to insert a board shape from Soldiworks with origin marks that matches exactly to the existing board shape.
Another issue I'm having is that because the board has a strange shape, it's difficult to manually set the origin because even when I click over a line, it's not right on top of it when I zoom in (has always a offset). The same principle applies when I try to mark the PCB's boundaries with simple pads or taking measures, which is the CADish way I explored to center an object between the board's lateral edges (horizontal boundaries), for example. Is there a different way to find the board's center and/or a way to place components on centerlines, midpoints or in the center of an component? When designing footprints (pcb library view) there is an option to center the origin between the existing pads but not on the layout. To get a more precise placement, I manually check the coordinates between the keep-out lines on the board edges and then make calculations, but this is not practical or error-proof.

[free_electron]

P-L  , click on the top boundary and then click the bottom boundary. this draws a vertical line edge-to-edge.
now click that line : the snap points will appear , place origin and click on that center snap point. this is the true midpoint.

[malrip]

Thank you very much. Does the job! I'm not sure why, but after making some changes to the view properties, I can now set the origin to be exactly on the board's edge (I didn't changed the snap grid).

[ajb]

Thank you very much. Does the job! I'm not sure why, but after making some changes to the view properties, I can now set the origin to be exactly on the board's edge (I didn't changed the snap grid).

It may be that you have your snap settings to only snap to the current layer, and were previously on a different layer than the object you were trying to snap to? 

[Pseudobyte]

Another way to do this is to select the component and the horizontal edge ( or the arc if the board is circular ). Press A C (align horizontal center) then select the edge. Then repeat the process for the vertical edge but this time using A V (align vertical center).