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How is the position property calculated after the anchor point is 0?

Community Beginner ,
May 18, 2024 May 18, 2024

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My question is, how is the position property calculated then after the anchor point has moved to 0? Is it calculated based on the shift of the layer content?

 

Initial Setup:

(transform effect)

Anchor Point: (540, 540)
Position: (540, 540)


Visual Position: The layer is centered in the composition.


Change Anchor Point:

Anchor Point: (0, 540)
Position: (540, 540)
Visual Position: The layer content shifts right by 540 pixels.

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Community Expert ,
May 19, 2024 May 19, 2024

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In After Effects, the position property of a layer is always calculated relative to its anchor point. When you move the anchor point of a layer, it changes the reference point for position calculations.

In your initial setup, with the anchor point at (540, 540) and position also at (540, 540), the layer is centered in the composition. This means that the position is calculated based on the center of the layer relative to the composition.

When you change the anchor point to (0, 540), but keep the position at (540, 540), the layer's content shifts right by 540 pixels. This shift occurs because the position property is still calculated relative to the anchor point. So, even though the position remains the same, the visual position of the layer changes because the anchor point has moved.

In essence, After Effects calculates the position property based on the distance between the anchor point and the layer's content. When you move the anchor point, it changes the reference point for this calculation, causing the layer's visual position to shift accordingly.

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Community Expert ,
May 19, 2024 May 19, 2024

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In more plain language:
A layer's Position property is actually the position of the layer's Anchor Point in the Composition space. 

 

Bonus:

When you parent one layer to another, the child layer's Position property is now showing you that layer's Anchor Point in the parent's layer space! This is why these values suddenly change when you parent, and why an expression on Position will often need to be modified based on whether a layer is parented or not. 

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Community Beginner ,
Jun 14, 2024 Jun 14, 2024

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Eyyy I know it's been a while but that actually solved my confusion, especially the child layer's position property in relationship to the parent layer's property. Explains why the position property changes when I parent a layer. 

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Valorous Hero ,
Jun 15, 2024 Jun 15, 2024

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Some good info here but perhaps a bit more will be helpful - 

When talking about Anchor Point and Position values, we are talking about distances or measuring a distance; from Point A to Point B or Start Point to End Point. When measuring distances, much like measuring with a ruler, we require two points of references.

IMPORTANT NOTES -
Point of Origin - this defines point [0,0] for a Composition and a Layer. When you look at a layer in the composition, you are essentially looking at TWO Coordinate Systems; one for the Composition and the other for the Layer. The Point of Origin is usually used as the Starting Point for calculating distances such as the Anchor Point and Position.

Composition Point of Origin - this is at the Top Left Corner of the Composition Window and has a Cartesian Product value of [0,0].

Layer Point of Origin - this differs between the Types of Layers in After Effects BUT they all have a default value of [0,0] - this distinctive [0,0] is a critical characteristic of a Point of Origin. For a Shape Layer, its Point of Origin is at the center of its Rectangular Boundary.

For a Solid/PNG/Video/Nested Composition, their Point of Origin is the Top Left corner of their respective Rectangular Boundary.



CALCULATING/UNDERSTANDING ANCHOR POINT AND POSITION VALUES

Anchor Point Value - this value is derived from its position relative to the layer's Point of Origin.

Position Value - this value is derived from its Anchor Point's position relative to the Composition's Point of Origin.

In a Parent-Child Hierarchy, the Child Layer's position value is its Anchor Point relative to the Parent Layer's Point of Origin since it now lives in the Parent Layer's space and not Composition Space.

HTH


Motion Graphics Brand Guidelines & Motion Graphics Responsive Design Toolkits

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