Exercise: Working with the Rhino API (2/3)

The ghpythonlib.components library

Now that we have correctly specified the type of the geometry we are inputting, we can start to build our simple script. We will start by importing the ghpythonlib.components library. Delete the previous two lines and type on the first line:

import ghpythonlib.components as ghcomp

This will import the components portion of the main ghpythonlib library into our script so we can use it’s methods to work with geometry. We use the import ... as ... syntax to give the library a shorter keyword that will save us typing and make the script cleaner. Now when we want to use the library we can reference it with ghcomp rather than typing the full ghpythonlib.components each time.

The ghpythonlib.components library contains methods that replicate the behavior of each component in Grasshopper. Each method expects the same number and type of inputs as its Grasshopper component equivalent, and returns the same outputs. If the component has more than one output the return will be a list whose length is the number of outputs.

Let’s use the library's Circle method to create a Circle based on a center Point and radius, just like the Circle component in Grasshopper. On the next line type:

a = ghcomp.Circle(x, 2)

As expected this creates a circle with a radius of 2, centered on the input point.

Creating a circle with Python

The Rhino.Geometry library

Now let’s do the same thing with the Rhino.Geometry library. Below the first import line, type:

import Rhino.Geometry as rh

This line imports the Geometry portion of the main Rhino library and assigns it the keyword rh. Now we can change the line of code that creates the circle to:

a = rh.Circle(x, 2)

If you run the script you will see that the result is exactly the same — a circle centered on our input point with a radius of 2.

The rhinoscriptsyntax library

Finally, let’s look at the same example using the rhinoscriptsyntax library. We can import the library by typing:

import rhinoscriptsyntax as rs

and use the library’s .AddCircle() method to create a new circle based on the input point and radius.

a = rs.AddCircle(x, 2)

We have now seen three different libraries that allow you to work with geometry in Python, so which one should you use? Ultimately all three do basically the same thing and create the same exact geometry, but they each come with certain benefits and limitations:

• The ghpythonlib.components library makes it easier to get started because you can directly use the same components you are used to using in Grasshopper. However you are restricted to what is available in Grasshopper, and some of the methods can be clunky compared to those in RhinoCommon.

• The rhinoscriptsyntax library was created to make it easier for those already used to using RhinoScript to transition to using Python. The methods in the rhinoscriptsyntax library replicate those in RhinoScript, but do so by ‘wrapping up’ methods from RhinoCommon. Thus they may make some geometric operations easier and cleaner, but also limit the scope of possibilities compared to using the full RhinoCommon.

• The Rhino.Geometry library is the most comprehensive and robust way to work with geometry in Python because it exposes all of the methods in the full RhinoCommon library. RhinoCommon is a universal cross-platform library developed by McNeel for the release of Rhino 5 which allows all versions of Rhino and Grasshopper to access the same geometric data types and methods. By tapping into this library we gain access to everything Rhino is capable of, which allows us to do things we could not do with either Grasshopper or RhinoScript.