From 72907566bbbb6f760e2fb7be02d22766ecf191cd Mon Sep 17 00:00:00 2001 From: philip Date: Thu, 2 Apr 2020 14:14:13 +0000 Subject: [PATCH] Add comment to explain calculation. --- src/ol/reproj/Triangulation.js | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/src/ol/reproj/Triangulation.js b/src/ol/reproj/Triangulation.js index b6091d149f..ba49bac8c4 100644 --- a/src/ol/reproj/Triangulation.js +++ b/src/ol/reproj/Triangulation.js @@ -139,6 +139,16 @@ class Triangulation { const sourceBottomRight = this.transformInv_(destinationBottomRight); const sourceBottomLeft = this.transformInv_(destinationBottomLeft); + /* + * The maxSubdivision controls how many splittings of the target area can + * be done. The idea here is to do a linear mapping of the target areas + * but the actual overal reprojection (can be) extremely non-linear. The + * default value of MAX_SUBDIVISION was chosen based on mapping a 256x256 + * tile size. However this function is also called to remap canvas rendered + * layers which can be much larger. This calculation increases the maxSubdivision + * value by the right factor so that each 256x256 pixel area has + * MAX_SUBDIVISION divisions. + */ const maxSubdivision = MAX_SUBDIVISION + (opt_destinationResolution ? Math.max(0, Math.ceil(Math.log2(getArea(targetExtent) / (opt_destinationResolution * opt_destinationResolution * 256 * 256))))