Trouble with bounding boxes

Currently I'm stuck on querying the bounding box for the CV curve. This will be needed to fit the river slope image map onto the curve in order to retrieve the slope value at a specific position.

In my compute() function, I have my MFnNurbsCurve object, via

MObject curve = inputCurveData.asNurbsCurve();
MFnNurbsCurve curveFn (curve, &returnStatus); // Can also set as MItCurveCV
McheckErr(returnStatus, "ERROR creating curve function set\n");

And I've tried directly calling boundingBox() on it (which should work since MFnNurbsCurve inherits from MFnDagNode), but I get a return status code of 1 (kFailure), and internal status code of 6 (kNotImplemented), which isn't very helpful. I still don't know why it's not working.

An alternate method I tried was to query the bounding box attribute, as follows:

MObject boundingBoxObj = curveFn.attribute(MString("boundingBox"), &returnStatus); 

I get the same error with this method.

I know the bounding box is definitely queryable because the MEL command getAttr curve1.boundingBoxMin returns a valid value. Though I would rather not resort to that if I don't have to.

EDIT:
Per this answer, it seems like the reason why boundingbox() has been failing is because it will only work if the MFnNurbsCurve is attached to a dagNode, rather than curve data coming through the DG. I'm just going to manually calculate the bounding box.