I suspect there is a well-known and easy to explain reason for the behavior I'm seeing, but I am having difficulty explaining it. (And likely not able to Google for the answer.)

When adding a child GameObject to a translated parent, the child's localPosition is modified so that the child's position stays the same AFTER the parent's transformation is applied. Is there a way to not have this be the case?

In the following example, I create a parent object and move it to (1,1,1), and then attach the child. I would like the child's position to be (1,1,1), that is (0,0,0) relative to the parent. However, the child's position is modified to be (-1,-1,-1) so that it is (0,0,0) relative to the world.

Here is a repro:

// Create parent.
GameObject parent = new GameObject();
parent.name = "Parent GameObject";
parent.transform.parent = foregroundObject.transform;

// Move the parent.
parent.transform.Translate(1, 1, 1);

// Add a child under the parent GameObject.
GameObject child = (GameObject) GameObject.Instantiate(guildiePrefab);
child.name = "Child GameObject";

child.transform.parent = parent.transform;

// PROBLEM: localPosition is set so that the "global" position is (0,0,0).
    // How can I add the child object and have its position be (1,1,1)?
this.Assert(child.transform.localPosition.ToString() == "(-1.0, -1.0, -1.0)");
this.Assert(child.transform.position.ToString() == "(0.0, 0.0, 0.0)");

Is there a different way I should be adding child as a child of parent? Or, should I always zero-out the position of parent before adding a child? (If that is the case, any reason why I need to do this? What is the rational for this design choice?)

I suspect there is a well-known and easy to explain reason for the behavior I'm seeing, but I am having difficulty explaining it (and likely not able to Google for the answer).

When adding a child GameObject to a translated parent, the child's localPosition is modified so that the child's position stays the same after the parent's transformation is applied. Is there a way to not have this be the case?

In the following example, I create a parent object and move it to (1,1,1), and then attach the child. I would like the child's position to be (1,1,1), that is (0,0,0) relative to the parent. However, the child's position is modified to be (-1,-1,-1) so that it is (0,0,0) relative to the world.

Here is a repro:

// Create parent.
GameObject parent = new GameObject();
parent.name = "Parent GameObject";
parent.transform.parent = foregroundObject.transform;

// Move the parent.
parent.transform.Translate(1, 1, 1);

// Add a child under the parent GameObject.
GameObject child = (GameObject) GameObject.Instantiate(guildiePrefab);
child.name = "Child GameObject";

child.transform.parent = parent.transform;

// PROBLEM: localPosition is set so that the "global" position is (0,0,0).
// How can I add the child object and have its position be (1,1,1)?
this.Assert(child.transform.localPosition.ToString() == "(-1.0, -1.0, -1.0)");
this.Assert(child.transform.position.ToString() == "(0.0, 0.0, 0.0)");

Is there a different way I should be adding child as a child of parent? Or, should I always zero-out the position of parent before adding a child? If that is the case, any reason why I need to do this? What is the rational for this design choice?