function Isocontour(params) {
    Transform.call(this, null, params);
  }
Generate isocontours (level sets) based on input raster grid data.
@constructor
@param {object} params - The parameters for this operator.
@param {function(object): *} [params.field] - The field with raster grid
  data. If unspecified, the tuple itself is interpreted as a raster grid.
@param {Array<number>} [params.thresholds] - Contour threshold array. If
  specified, the levels, nice, resolve, and zero parameters are ignored.
@param {number} [params.levels] - The desired number of contour levels.
@param {boolean} [params.nice] - Boolean flag indicating if the contour
  threshold values should be automatically aligned to "nice"
  human-friendly values. Setting this flag may cause the number of
  thresholds to deviate from the specified levels.
@param {string} [params.resolve] - The method for resolving thresholds
  across multiple input grids. If 'independent' (the default), threshold
  calculation will be performed separately for each grid. If 'shared', a
  single set of threshold values will be used for all input grids.
@param {boolean} [params.zero] - Boolean flag indicating if the contour
  threshold values should include zero.
@param {boolean} [params.smooth] - Boolean flag indicating if the contour
  polygons should be smoothed using linear interpolation. The default is
  true. The parameter is ignored when using density estimation.
@param {boolean} [params.scale] - Optional numerical value by which to
  scale the output isocontour coordinates. This parameter can be useful
  to scale the contours to match a desired output resolution.
@param {string} [params.as='contour'] - The output field in which to store
  the generated isocontour data (default 'contour').