Multiresolution streamline placement for 2D flow fields

Streamline is a popular choice to visualize flow fields, but it not easy to determine the number and the distribution of streamlines. In this paper, a multiresolution streamline placement method is presented to visualize 2D flow fields at different levels of detail. Each level has different number of streamlines that are uniformly distributed in the field at different resolutions. This method is implemented by constructing a hierarchy of control grids to manipulate the procedure of placement. The top level of the hierarchy is the coarsest control grid whose cell size is predefined. Using this grid and a centroid-based seeding strategy, a sparse placement is obtained, where streamlines are evenly-spaced. Then, this sparse placement is changed into the next lower level by adding some new streamlines within the gaps of all existing streamlines under the control of a finer control grid. Although the total number of streamlines is increased, the original uniformity is not destroyed. The resolution and the density of streamlines are both improved from one level to its next lower level. This refinement between adjacent levels can be repeated until a suitable placement is obtained. Corresponding to the control grids, a hierarchy of streamline placements with different resolutions is also built up during the multiresolution analysis. It gives an opportunity to select suitable streamline placements with desired resolutions. And it also provides a new way to have an insight into the flow field at different scales. Test results show that this multiresolution streamline placement is valid and efficient.