Use custom class as a parameter of a function

I write a library using c#. I want to use a function in the dll.
I define a function like below
public static bool Zoom(DPoint3d pdMin, DPoint3d pdMax, DPoint3d pdCenter, double dFactor, bool b_execute = true)

DPoint3d is a custom class.
When I use it in the Dynamo, the parameter becomes a var type.

I want to use DPoint instead. How can I do that? Thanks!

you will need to post some context here. I have no clue what you are trying to do. Also please format snippets of code so that they show up correctly instead of being displayed as text.