One or more non-transitory computer readable media having instructions stored thereon, for execution by a computer that includes a graphical user interface and a user input device , the instructions to perform a method comprising: displaying a graphical representation of an anatomic structure on the graphical user interface , the graphical representation of the anatomic structure being determined from a geometry of the anatomic structure and wherein geometric knots are determined at respective positions along a centerline of the graphical representation of the anatomic structure; determining a location parameter for a graphical marker along the graphical representation of the anatomic structure in response to a first user input from the user input device, wherein the location parameter for the graphical marker corresponds to spatial coordinates for a closest geometric knot of the geometric knots, and wherein the graphical marker represents a location of an anatomic opening between the anatomical structure and another adjacent fluidly connected anatomical structure; displaying the graphical marker relative to the graphical representation of the anatomic structure on the graphical user interface based on the location parameter; changing the location parameter to move the graphical marker along the graphical representation of the anatomic structure based on a user input from a user input device ; selecting a fixed location along the graphical representation of the anatomic reference to fix the graphical marker relative to the graphical representation of the anatomic structure in response to a second user input from the user input device ; and generating an output visualization that includes at least one view of the graphical representation of the anatomic structure and the graphical representation of the graphical marker at the fixed location. displaying a graphical representation of an anatomic structure on the graphical user interface , the graphical representation of the anatomic structure being determined from a geometry of the anatomic structure and wherein geometric knots are determined at respective positions along a centerline of the graphical representation of the anatomic structure; determining a location parameter for a graphical marker along the graphical representation of the anatomic structure in response to a first user input from the user input device, wherein the location parameter for the graphical marker corresponds to spatial coordinates for a closest geometric knot of the geometric knots, and wherein the graphical marker represents a location of an anatomic opening between the anatomical structure and another adjacent fluidly connected anatomical structure; displaying the graphical marker relative to the graphical representation of the anatomic structure on the graphical user interface based on the location parameter; changing the location parameter to move the graphical marker along the graphical representation of the anatomic structure based on a user input from a user input device ; selecting a fixed location along the graphical representation of the anatomic reference to fix the graphical marker relative to the graphical representation of the anatomic structure in response to a second user input from the user input device ; and generating an output visualization that includes at least one view of the graphical representation of the anatomic structure and the graphical representation of the graphical marker at the fixed location. <EOS>