Categories

# Make Circular Array objects face the Center using Geometry Nodes in Blender

In this tutorial, we are going to make the Instance objects face the center. We already have made a circular Array. We are going to use a mathematical formula to find out the value of angle. Blender version 2.93 is used.

In this tutorial, we are going to make the Instance objects face the center. We already have made a circular Array. We are going to use a mathematical formula to find out the value of angle. Blender version 2.93 is used.

In the previous tutorial, made a simple circular array using Geometry nodes. This is the continuation of that tutorial.

## Mathematical formula for angle

To make the instance objects face the center, we are going to use the following Mathematical formula:

`θ` is the angle which we have to rotate. `y `and `x `are the positional values of the Cartesian Coordinate system(XYZ). `Arctangent `is the mathematical operation being performed. All of this can be done using geometry nodes.

First, we have obtain x and y values. To do this, we are going to use Attribute Separate XYZ node. It separates the value of X,Y and Z from the Vector.

Add the Attribute Separate XYZ by clicking `Add > Attribute > Attribute Separate XYZ`. Place it between Circle and Point Instance Node.

In the `Vector` attribute of the node, type `position`, and type `x`, `y `and `z `in the Result X, Y and Z parameters. `position` is a built-in attribute that shows the position of the points.

We have obtained x and y position values for every instance. Now, according to the formula, we need to divide y values by x.

## Applying Mathematical formula using Geometry Nodes

We are going to apply the mathematical formula step by step.

1. Divide y by x
2. Obtain the angle using arctangent mathematical operation.
3. Rotate the objects.

### Add Attribute Math for Division

For this purpose, we will use Attribute Math node. Add an Attribute Math node by clicking `Add > Attribute > Attribute Math`. Place the node between Attribute Separate XYZ and Point Instance nodes.

Change the Operation to `Divide`. Both `A `and `B `values should be set to `Attribute`. In this case, A is the numerator while B is the Denominator.

As it is in formula, we are going to divide Y values by X values. So, in the `A `attribute, we write `y`, and in the `B `parameter we write `x`. Finally, we store these values in another parameter, which we call “angle”.

angle is not a built in attribute, rather it is a custom attribute.

We need to perform Arctangent mathematical operation on the angle attribute.

## Add Attribute Math node for Arctangent operation

So, we add another `Attribute Math node`, change the operation to `Arctangent`. We type angle in `A`, so the mathematical operation is performed on the attribute A.

We type `angle `in `Result `attribute so, that the output value is stored in the same attribute angle.

## Add Point Rotate for Rotation of objects

Now, we need to rotate the instances, to do that, we add Point Rotate node. Click `Add > Point > Point Rotate`. Place it between Attribute Math node and the Point Instance node.

Choose the `Axis angle` to be `Z`. The Value of Z in the Axis Vector should be `1 `and the other values should be `0`.

Type `angle `in the `Angle `attribute.

We see that the instances do not face the center, rather they face the adjacent instances. Basically, the angle is off by a 90 degrees. So, to fix this, we add 90 degrees to our instances.

## Add 90 degrees using Attribute Math node

We add another `Attribute Math` node just before the Point Rotate node, select the operation to `Add`, choose `A `to be an `Attribute `while `B `is a `Float`. We add 90 degrees.

In the `A` attribute we type the `angle `attribute, in the `B`, we type `1.571 radians` which is equivalent of `90` degrees.

## Half the objects not facing the center

We see that half of the instances are facing the center while the other half is off by a 180 degrees.

This problem is because when of the negative value of x. Half of the instance objects are on positive X axis while half of the instances are on negative X axis.

When there is an instance object that is on the negative X axis. It gets off by a 180 degrees.

To fix this, we need to add 180 degrees to those instance objects.

This is the Geometry node setup so far.

In the next tutorial, we are going to add a Frame nodes in Geometry Nodes. We are going to do this to stay organized in so many nodes. And after that tutorial, we will fix Circular array for X value less than 0 using Geometry Nodes.

Here are more parts of this tutorial series:

Use SUMIF function in MS Excel