![]() Apply linear interpolation between the original field data values to find the exact position of the contour line along the edges of the cell. ![]() Use the cell index to access a pre-built lookup table with 16 entries listing the edges needed to represent the cell (shown in the lower right part of the picture below).The resulting 4-bit index can have 16 possible values in the range 0–15. Compose the 4 bits at the corners of the cell to build a binary index: walk around the cell in a clockwise direction appending the bit to the index, using bitwise OR and left-shift, from most significant bit at the top left, to least significant bit at the bottom left.Note that this contouring grid is one cell smaller in each direction than the original 2D field. 0 where the data value is below the isovalueĮvery 2x2 block of pixels in the binary image forms a contouring cell, so the whole image is represented by a grid of such cells (shown in green in the picture below).1 where the data value is above the isovalue.Apply linear interpolation along the boundaries of the cell to calculate the exact contour position.Īpply a threshold to the 2D field to make a binary image containing:.Use a pre-built lookup table, keyed on the cell index, to describe the output geometry for the cell.Calculate a cell index using comparisons of the contour level(s) with the data values at the cell corners.Process each cell in the grid independently.Marching squares takes a similar approach to the 3D marching cubes algorithm: Typical applications include the contour lines on topographic maps or the generation of isobars for weather maps. Isobands – filled areas between isolines.Isolines – lines following a single data level, or isovalue.A similar method can be used to contour 2D triangle meshes. In computer graphics, marching squares is an algorithm that generates contours for a two-dimensional scalar field (rectangular array of individual numerical values). ( February 2022) ( Learn how and when to remove this template message) Please help to improve this article by introducing more precise citations. This article includes a list of references, related reading, or external links, but its sources remain unclear because it lacks inline citations.
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