# The .obj model file is offset far from the world origin,However, it is still possible to achieve position-based interaction between the image and the model 

**URL:** <https://discourse.slicer.org/t/the-obj-model-file-is-offset-far-from-the-world-origin-however-it-is-still-possible-to-achieve-position-based-interaction-between-the-image-and-the-model/42422>\
**Category:** Development\
**Created:** [April 3, 2025, 12:56pm UTC](https://discourse.slicer.org/t/the-obj-model-file-is-offset-far-from-the-world-origin-however-it-is-still-possible-to-achieve-position-based-interaction-between-the-image-and-the-model/42422 "2025-04-03T12:56:54Z")\
**Posts on this page:** 7\
**Page:** 1

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**Author:** ![jiajiadelequ](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.slicer.org/jiajiadelequ/32/79895_2.png) [@jiajiadelequ](https://discourse.slicer.org/u/jiajiadelequ)\
**Post date:** [April 3, 2025, 12:56pm UTC](https://discourse.slicer.org/t/the-obj-model-file-is-offset-far-from-the-world-origin-however-it-is-still-possible-to-achieve-position-based-interaction-between-the-image-and-the-model/42422/1 "2025-04-03T12:56:54Z")

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![图片1](https://us1.discourse-cdn.com/flex002/uploads/slicer/original/3X/1/6/1649ee8c363ea0efd1cdea8b275adc5fc0b9200c.png)  
I have a set of matching .nii image files and .obj model files. After importing them into 3D Slicer, I found that the .obj model file is offset far from the world origin, basically out of the image’s range in the world coordinate system. However, it is still possible to achieve position-based interaction between the image and the model. How is this accomplished?

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**Author:** ![lassoan](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.slicer.org/lassoan/32/13_2.png) [@lassoan](https://discourse.slicer.org/u/lassoan)\
**Post date:** [April 3, 2025, 12:59pm UTC](https://discourse.slicer.org/t/the-obj-model-file-is-offset-far-from-the-world-origin-however-it-is-still-possible-to-achieve-position-based-interaction-between-the-image-and-the-model/42422/2 "2025-04-03T12:59:34Z")

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Could you take a screenshot with the slice views visible in 3D so that we can see where the image is? (click the pushpin and then the eye icon above each slice view).

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**Author:** ![jiajiadelequ](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.slicer.org/jiajiadelequ/32/79895_2.png) [@jiajiadelequ](https://discourse.slicer.org/u/jiajiadelequ)\
**Post date:** [April 7, 2025, 2:07am UTC](https://discourse.slicer.org/t/the-obj-model-file-is-offset-far-from-the-world-origin-however-it-is-still-possible-to-achieve-position-based-interaction-between-the-image-and-the-model/42422/3 "2025-04-07T02:07:02Z")

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![image](https://us1.discourse-cdn.com/flex002/uploads/slicer/original/3X/c/5/c59d2f925e753f75459f7a459cf4a4174911a5fd.jpeg)  
However, when I load these .obj models into my self-written VTK software, the displayed positions are significantly offset from the origin, and there is a large discrepancy between the positions selected on the image and the model.  
 ![image](https://us1.discourse-cdn.com/flex002/uploads/slicer/original/3X/0/0/001292a3541ff9e0ecc57d3752d8be8e3f10bf3e.jpeg)

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**Author:** ![jiajiadelequ](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.slicer.org/jiajiadelequ/32/79895_2.png) [@jiajiadelequ](https://discourse.slicer.org/u/jiajiadelequ)\
**Post date:** [April 7, 2025, 2:09am UTC](https://discourse.slicer.org/t/the-obj-model-file-is-offset-far-from-the-world-origin-however-it-is-still-possible-to-achieve-position-based-interaction-between-the-image-and-the-model/42422/4 "2025-04-07T02:09:23Z")

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This is the relevant code I wrote

```auto
void vtkSliceLoader::Load(std::string fileName)
{
    reader->SetFileName(fileName.c_str());
    reader->Update();

    //计算center
    double spacing[3];
    double origin[3];
    int extent[6];
    reader->GetOutputInformation(0)->Get(
        vtkStreamingDemandDrivenPipeline::WHOLE_EXTENT(), extent);
    reader->GetOutput()->GetSpacing(spacing);
    reader->GetOutput()->GetOrigin(origin);
    this->center[0] = origin[0] + spacing[0] * 0.5 * (extent[0] + extent[1]);
    this->center[1] = origin[1] + spacing[1] * 0.5 * (extent[2] + extent[3]);
    this->center[2] = origin[2] + spacing[2] * 0.5 * (extent[4] + extent[5]);
}
```

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<div class="post-metadata">

**Author:** ![jiajiadelequ](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.slicer.org/jiajiadelequ/32/79895_2.png) [@jiajiadelequ](https://discourse.slicer.org/u/jiajiadelequ)\
**Post date:** [April 7, 2025, 2:10am UTC](https://discourse.slicer.org/t/the-obj-model-file-is-offset-far-from-the-world-origin-however-it-is-still-possible-to-achieve-position-based-interaction-between-the-image-and-the-model/42422/5 "2025-04-07T02:10:38Z")

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```auto
void asclepios::gui::vtkResliceCallback::moveCursor(double* t_position) const
{
	vtkMatrix4x4* matrix = nullptr;
	vtkMatrix4x4* matrix2 = nullptr;
	vtkMatrix4x4* sourceMatrix =
		m_resliceWidget->getImageReslicers()[m_handleNumber]->GetResliceAxes();
	switch (m_handleNumber)
	{
	case 0:
		matrix = m_resliceWidget->getImageReslicers()[1]->GetResliceAxes();
		matrix2 = m_resliceWidget->getImageReslicers()[2]->GetResliceAxes();
		break;
	case 1:
		matrix = m_resliceWidget->getImageReslicers()[0]->GetResliceAxes();
		matrix2 = m_resliceWidget->getImageReslicers()[2]->GetResliceAxes();
		break;
	case 2:
		matrix = m_resliceWidget->getImageReslicers()[0]->GetResliceAxes();
		matrix2 = m_resliceWidget->getImageReslicers()[1]->GetResliceAxes();
		break;
	default:
		break;
	}
	if (m_window)
	{
		vtkNew<vtkTransform> transform;
		transform->SetMatrix(sourceMatrix);
		transform->Translate(t_position[0], t_position[1], 0);
		double center[3] =
		{
			transform->GetMatrix()->GetElement(0, 3),
			transform->GetMatrix()->GetElement(1, 3),
			transform->GetMatrix()->GetElement(2, 3)
		};
		matrix->SetElement(0, 3, center[0]);
		matrix->SetElement(1, 3, center[1]);
		matrix->SetElement(2, 3, center[2]);
		matrix2->SetElement(0, 3, center[0]);
		matrix2->SetElement(1, 3, center[1]);
		matrix2->SetElement(2, 3, center[2]);

		
		emit EventManager::instance()->moveCursor(m_handleNumber,center);
	}
}
```

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<div class="post-metadata">

**Author:** ![jiajiadelequ](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.slicer.org/jiajiadelequ/32/79895_2.png) [@jiajiadelequ](https://discourse.slicer.org/u/jiajiadelequ)\
**Post date:** [April 7, 2025, 2:10am UTC](https://discourse.slicer.org/t/the-obj-model-file-is-offset-far-from-the-world-origin-however-it-is-still-possible-to-achieve-position-based-interaction-between-the-image-and-the-model/42422/6 "2025-04-07T02:10:54Z")

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```auto
void vtkThreeDViewerLogic::onSliceMoveCursor(int handleIdx, double* slicePos) {

    double worldPoint[3];
    double* center = vtkSliceLoader::instance().GetCenter();
 
    worldPoint[0] = slicePos[0] - center[0];
    worldPoint[1] = slicePos[1] - center[1];
    worldPoint[2] = slicePos[2] - center[2];

    if (!mRenderer->HasViewProp(mPickMark)) {
        mRenderer->AddActor(mPickMark);
    }

    mPickMark->SetPosition(worldPoint);
    mInteractor->Render();
}
```

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<div class="post-metadata">

**Author:** ![lassoan](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.slicer.org/lassoan/32/13_2.png) [@lassoan](https://discourse.slicer.org/u/lassoan)\
**Post date:** [April 7, 2025, 4:00am UTC](https://discourse.slicer.org/t/the-obj-model-file-is-offset-far-from-the-world-origin-however-it-is-still-possible-to-achieve-position-based-interaction-between-the-image-and-the-model/42422/7 "2025-04-07T04:00:35Z")

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The code snippets are incomplete, it is not possible to even guess what they might be doing.  
Slicer is open-source, you can inspect the code and figure out what it does and reimplement in your own software. However, you will experience that there is just way too much to copy from Slicer - you are probably better off customizing and extending Slicer - see [https://www.kitware.com/slicercat-creating-custom-applications-based-on-3d-slicer/](https://www.kitware.com/slicercat-creating-custom-applications-based-on-3d-slicer/)