[WIP - DONT MERGE] fix(fov): fov was not working correctly for other planes

[IbrahimCSAE]

Context

The old code was not determining correctly which extent dimensions to use based on the view plane normal, now its fixed to use:

• Sagittal (looking along X): uses Y extent for width, Z extent for height
• Coronal (looking along Y): uses X extent for width, Z extent for height
• Axial (looking along Z): uses X extent for width, Y extent for height

[sedghi]

Looks reasonable

[tblock79]

This fix seems to break the stack viewports in many cases, and I am not sure if it would work for volumes with oblique orientation.

Using the legacy FOV calculation method for volume viewports could possibly be a quick fix:

if (imageData && !useLegacyMethod && (this.type !== ViewportType.ORTHOGRAPHIC)) {
    const extent = imageData.getExtent();
    const spacing = imageData.getSpacing();
    widthWorld = (extent[1] - extent[0]) * spacing[0];
    heightWorld = (extent[3] - extent[2]) * spacing[1];
}
else {
    ({ widthWorld, heightWorld } = this._getWorldDistanceViewUpAndViewRight(bounds, viewUp, viewPlaneNormal));
}

[IbrahimCSAE]

This fix seems to break the stack viewports in many cases, and I am not sure if it would work for volumes with oblique orientation.

Using the legacy FOV calculation method for volume viewports could possibly be a quick fix:

if (imageData && !useLegacyMethod && (this.type !== ViewportType.ORTHOGRAPHIC)) {

    const extent = imageData.getExtent();

    const spacing = imageData.getSpacing();

    widthWorld = (extent[1] - extent[0]) * spacing[0];

    heightWorld = (extent[3] - extent[2]) * spacing[1];

}

else {

    ({ widthWorld, heightWorld } = this._getWorldDistanceViewUpAndViewRight(bounds, viewUp, viewPlaneNormal));

}

Yeah this is broken thats why we changed the title to WIP. We could do legacy for Volume viewport but I believe it still doesn't always make the image take the full canvas. I'm leaving it up until we figure out something consistent

[tblock79]

That's definitely true. Using the legacy scaling as fallback might still make sense for the interim time because the current release version is often cropping a significant number of slices in volume viewports (thus, the legacy scaling should be preferable - even if not perfect).

[sedghi]

can you send us some screenshots of how much is it missing?

[tblock79]

Sure, here is an example (left is the current release, right is when using the legacy method as fallback for volume viewports). As you can see, a significant number of slices is outside the FOV after a camera reset. The impact might be dataset-dependent but I noticed it quite often.

[sedghi]

I think this is related issue #2168

[wayfarer3130]

@IbrahimCSAE - can you tell me exactly how to reproduce the issue in this PR? I've tweaked the PR to just compute the delta between your method and the current method and I'm see differences of less than 0.0001
@sedghi - unless we can get reproduction steps, I think this item can be closed.

[sedghi]

@wayfarer3130 i remember the neptune study in MPR showed the issue regarding initial fov of reconstruction views

[IbrahimCSAE]

@IbrahimCSAE - can you tell me exactly how to reproduce the issue in this PR? I've tweaked the PR to just compute the delta between your method and the current method and I'm see differences of less than 0.0001 @sedghi - unless we can get reproduction steps, I think this item can be closed.

I don’t have clean repro steps beyond what Tobias originally reported, and it’s been a while since I last dug into this. I agree the delta you’re seeing is tiny.

What I’m proposing is to keep the old FOV logic for volume viewports, and keep the current/improved logic for stack viewports, so we don’t regress the stack behavior.

This is what I was proposing (and what @tblock79 also suggested):

if (imageData && viewport instanceof StackViewport) {
  const extent = imageData.getExtent();
  const spacing = imageData.getSpacing();

  widthWorld = (extent[1] - extent[0]) * spacing[0];
  heightWorld = (extent[3] - extent[2]) * spacing[1];
} else {
  ({ widthWorld, heightWorld } = this._getWorldDistanceViewUpAndViewRight(
    bounds,
    viewUp,
    viewPlaneNormal
  ));
}

That way we don’t lose the improved FOV behavior for stack viewports, while restoring volume viewports to the old behavior.