# In doubly connected edge list how to link halfedges properly I’m working on doubly connected edge list. In the image below I need to add a new edge (consisting of halfedges $$g$$ and $$h$$). When adding a new edge we need to assign each half edge a previous and next half edges. In this example edge $$g$$ would have halfedge $$f$$ and $$h$$ as previous and next halfedges respectively. And edge $$h$$ would have halfedge $$g$$ and $$a$$ as previous and next halfedges respectively. If we ignore for a second them being linked to each other, $$g$$ and $$h$$ are linked to the pair $$f$$ and $$a$$. I hope this makes sense. My question is when adding a new edge, how do we know how to choose the correct pair to link to? In this example we could link our halfedges to the pair $$a, f$$ or $$c,b$$, or $$e,d$$. Do we have to resort to linear algebra, doing cross/dot product calculations to calculate what pair of halfedges to choose, based on the geometry of the edges? Am I possibly going in the completely wrong direction?

To get the potential canditates of pair of halfedges to link to, I iterate through all halfedges linked to vertex $$v$$, which here would be $$a,c,e$$ and for each I find the previous halfedge which would $$f, b,d$$ respectively.  Posted on Categories proxies