Frequently Asked Questions

version: V1.2.3

How to determine reciprocal primitive vectors (PRVs)?

HELIS shows a grid in spectrum to assist users in determining PRVs. When users select two base vectors, the system instantly generates a grid as a marking tool that should cover all visible diffraction spots. If any spots are missed, the selection is likely incorrect, and users should adjust their selection until all spots are covered by the grid. Note that high-frequency diffraction points are typically less affected by the missing wedge effect; therefore, we recommend selecting PRVs that align with high-frequency points. Additionally, the optimization method is generally useful for finding the correct result around user-selected PRVs.

How to select helical structures?

We recommend selecting helical structures with a specific angle (approximately 15 to 75 degrees) between the helical axis and the tilt axis of the tomogram. Helical structures nearly perpendicular to the tilt axis will have poor contrast, making it difficult to determine the center. Structures nearly parallel to the tilt axis will be most affected by the missing wedge effect at most diffraction points, which increases the difficulty of determining PRVs.

How many points are required to define a filament?

We recommend using a moderate number of label points. The distance between adjacent points had better be approximately 50 pixels or more. HELIS treats the label points as reliable data and performs only interpolation without smoothing or filtering. If users specify too many points with very short distances, the fitting of these points may result in high-frequency waves in the filament axis.