For questions please refer to the page numbers of the paper on my homepage. Q--Will Bernstein-Bezier coeficients and control points be constructed for the vertex type P which is the centroid of mesh face? A --Yes. Centroids are treated like original points This also answers your question Q--about "determining coefficients by analogous construction at the other subcell vertex of type P" Q -- In Figure 2.3 on page 7, two of five layers of Bernstein- Bezier coefficietns are shown. But I can't understand how the other three layers of coefficients can be found. Benjamin ( Hong Kong ) A -- The construction is symmetric. Thus, if you understand how to generate b_{ji} for j \in {0,1}, i\in {0,1,2,3,4} you also have the formulas for b_{ij}; this is explained for the case b_{12} and b_{21} on the page. Now you are still missing b_{ij} for i,j >= 2. However the construction is symmetric with respect to the original point P and the centroid. That is you also have the formulas for b_{ij} for i,j >= 2 (b_{22} is explicitely set to C_i, but you can choose some average of surrounding coefficients as well) Q -- In page 7 of your paper, in finding both b12,i and b21,i+1, there is 'j' there, I would like to ask what's the meaning oj it and how it related to 'i'. c3801040@comp.polyu.edu.hk A -- Look at Figure 2.3 directly below the formulas. The $i$th neighbor of $P$, $M_i$, has the surrounding panels labelled by $j$ as indicated. Q -- $M_i$, has the surrounding panels labelled by $j$ as indicated in the diagram, but how to determine which one of the four sections is Ci1, ...C14. It's because I can find the general relation between Cij and Ci. A-- Figure 2.3 indicates that C_i = C_{ij}; the labelling is relative to this identity. Q -- How to find b14,i? You seems to be not mention in thr paper. A -- Well, b_{03,i} is defined. By symmetry of the labelling you have the formula for b_{03,i-1} = b_{30,i} and by choosing P to be the other vertex of the 4-sided sub-panel, b_{14,i} is defined. A -- 1. c does not change meaning 2. boundaries are a whole chapter by themselves. I usually interpolate the boundary polygon. 3. I use mathematically positive orientation -- but any consistent orientation will do. Q -- Also, in the paper, you said that 'there exist a projection of its vertices into a plane such that none of the projected vertices lies in the convex hull of the other project vertices' Can you explain more on this? A -- The statement is precise. If flat, the panels should be convex.