12/25/2023 0 Comments Contour mapDensity EstimationĬonstructs a new density estimator with the default settings.Įstimates the density contours for the given array of data, returning an array of GeoJSON MultiPolygon geometry objects. If a count is specified instead of an array of thresholds, then the input values’ extent will be uniformly divided into approximately count bins see d3.ticks. Thus, there is exactly one generated MultiPolygon geometry object for each specified threshold value the threshold value is exposed as geometry.value. The first generated contour corresponds to the area where the input values are greater than or equal to x0 the second contour corresponds to the area where the input values are greater than or equal to x1, and so on. Thresholds are defined as an array of values. If thresholds is not specified, returns the current threshold generator, which by default implements Sturges’ formula. If thresholds is specified, sets the threshold generator to the specified function or array and returns this contour generator. If smooth is not specified, returns the current smoothing flag, which defaults to true. If smooth is specified, sets whether or not the generated contour polygons are smoothed using linear interpolation. If size is not specified, returns the current size which defaults to. The size is specified as an array where n is the number of columns in the grid and m is the number of rows n and m must be positive integers. If size is specified, sets the expected size of the input values grid to the contour generator and returns the contour generator. The input values must be an array of length n× m where is the contour generator’s size furthermore, each values must represent the value at the position ⟨ i, j⟩. The returned geometry objects are typically passed to d3.geoPath to display, using null or d3.geoIdentity as the associated projection.Ĭomputes a single contour, returning a GeoJSON MultiPolygon geometry object representing the area where the input values are greater than or equal to the given threshold value the threshold value for each geometry object is exposed as geometry.value. pow ( 2, i + 2 ) ) ) ( values ) // See function goldsteinPrice ( x, y ) const n = 256, m = 256, values = new Array ( n * m ) for ( let j = 0.5, k = 0 j Math. Populate a grid of n×m values where -2 ≤ x ≤ 2 and -2 ≤ y ≤ 1. For vanilla HTML in modern browsers, import d3-contour from Skypack: You can also download the latest release on GitHub. Here is a scatterplot showing the relationship between the idle duration and eruption duration for Old Faithful:Īnd here is a density contour plot showing the relationship between the weight and price of 53,940 diamonds: This library implements fast two-dimensional kernel density estimation see d3.contourDensity. Here is the Goldstein–Price function (a test function for global optimization) and a trippy animation of sin( x + y) sin( x - y):Ĭontours can also show the estimated density of point clouds, which is especially useful to avoid overplotting in large datasets. Here the above contours of surface temperature are displayed in the Natural Earth projection:Ĭontour plots can also visualize continuous functions by sampling. Since the contour polygons are GeoJSON, you can transform and display them using standard tools see d3.geoPath, d3.geoProject and d3.geoStitch, for example. Here is an example that loads a GeoTIFF of surface temperatures, and another that blurs a noisy monochrome PNG to produce smooth contours of cloud fraction: The geometry is in planar coordinates, where ⟨ i + 0.5, j + 0.5⟩ corresponds to element i + jn in the input values array. For example, here is Maungawhau’s topology (the classic volcano dataset and lors from R):įor each threshold value, the contour generator constructs a GeoJSON MultiPolygon geometry object representing the area where the input values are greater than or equal to the threshold value. This library computes contour polygons by applying marching squares to a rectangular array of numeric values.
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