Assume limited precision when rounding

src/ol/math.js

@@ -204,3 +204,47 @@ export function modulo(a, b) {
 export function lerp(a, b, x) {
   return a + x * (b - a);
 }
+
+/**
+ * Returns a number with a limited number of decimal digits.
+ * @param {number} n The input number.
+ * @param {number} decimals The maximum number of decimal digits.
+ * @return {number} The input number with a limited number of decimal digits.
+ */
+export function toFixed(n, decimals) {
+  const factor = Math.pow(10, decimals);
+  return Math.round(n * factor) / factor;
+}
+
+/**
+ * Rounds a number to the nearest integer value considering only the given number
+ * of decimal digits (with rounding on the final digit).
+ * @param {number} n The input number.
+ * @param {number} decimals The maximum number of decimal digits.
+ * @return {number} The nearest integer.
+ */
+export function round(n, decimals) {
+  return Math.round(toFixed(n, decimals));
+}
+
+/**
+ * Rounds a number to the next smaller integer considering only the given number
+ * of decimal digits (with rounding on the final digit).
+ * @param {number} n The input number.
+ * @param {number} decimals The maximum number of decimal digits.
+ * @return {number} The next smaller integer.
+ */
+export function floor(n, decimals) {
+  return Math.floor(toFixed(n, decimals));
+}
+
+/**
+ * Rounds a number to the next bigger integer considering only the given number
+ * of decimal digits (with rounding on the final digit).
+ * @param {number} n The input number.
+ * @param {number} decimals The maximum number of decimal digits.
+ * @return {number} The next bigger integer.
+ */
+export function ceil(n, decimals) {
+  return Math.ceil(toFixed(n, decimals));
+}

src/ol/source/ImageWMS.js

@@ -12,6 +12,7 @@ import {appendParams} from '../uri.js';
 import {assert} from '../asserts.js';
 import {assign} from '../obj.js';
 import {calculateSourceResolution} from '../reproj.js';
+import {ceil, floor, round} from '../math.js';
 import {compareVersions} from '../string.js';
 import {
   containsExtent,
@@ -22,6 +23,12 @@ import {
 } from '../extent.js';
 import {get as getProjection, transform} from '../proj.js';
 
+/**
+ * Number of decimal digits to consider in integer values when rounding.
+ * @type {number}
+ */
+const DECIMALS = 4;
+
 /**
  * @const
  * @type {import("../size.js").Size}
@@ -197,8 +204,8 @@ class ImageWMS extends ImageSource {
     };
     assign(baseParams, this.params_, params);
 
-    const x = Math.floor((coordinate[0] - extent[0]) / resolution);
-    const y = Math.floor((extent[3] - coordinate[1]) / resolution);
+    const x = floor((coordinate[0] - extent[0]) / resolution, DECIMALS);
+    const y = floor((extent[3] - coordinate[1]) / resolution, DECIMALS);
     baseParams[this.v13_ ? 'I' : 'X'] = x;
     baseParams[this.v13_ ? 'J' : 'Y'] = y;
 
@@ -290,17 +297,19 @@ class ImageWMS extends ImageSource {
     const imageResolution = resolution / pixelRatio;
 
     const center = getCenter(extent);
-    const viewWidth = Math.ceil(getWidth(extent) / imageResolution);
-    const viewHeight = Math.ceil(getHeight(extent) / imageResolution);
+    const viewWidth = ceil(getWidth(extent) / imageResolution, DECIMALS);
+    const viewHeight = ceil(getHeight(extent) / imageResolution, DECIMALS);
     const viewExtent = getForViewAndSize(center, imageResolution, 0, [
       viewWidth,
       viewHeight,
     ]);
-    const requestWidth = Math.ceil(
-      (this.ratio_ * getWidth(extent)) / imageResolution
+    const requestWidth = ceil(
+      (this.ratio_ * getWidth(extent)) / imageResolution,
+      DECIMALS
     );
-    const requestHeight = Math.ceil(
-      (this.ratio_ * getHeight(extent)) / imageResolution
+    const requestHeight = ceil(
+      (this.ratio_ * getHeight(extent)) / imageResolution,
+      DECIMALS
     );
     const requestExtent = getForViewAndSize(center, imageResolution, 0, [
       requestWidth,
@@ -327,8 +336,14 @@ class ImageWMS extends ImageSource {
     };
     assign(params, this.params_);
 
-    this.imageSize_[0] = Math.round(getWidth(requestExtent) / imageResolution);
-    this.imageSize_[1] = Math.round(getHeight(requestExtent) / imageResolution);
+    this.imageSize_[0] = round(
+      getWidth(requestExtent) / imageResolution,
+      DECIMALS
+    );
+    this.imageSize_[1] = round(
+      getHeight(requestExtent) / imageResolution,
+      DECIMALS
+    );
 
     const url = this.getRequestUrl_(
       requestExtent,