diff --git a/CHANGES.md b/CHANGES.md
index 7fef41d6a2b3..3e4dd65d9249 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -13,6 +13,7 @@
 - Fixed a bug where a removed billboard could prevent changing of the `TerrainProvider`. [#8766](https://github.com/CesiumGS/cesium/pull/8766)
 - Fixed an issue with 3D Tiles point cloud styling where `${feature.propertyName}` and `${feature["propertyName"]}` syntax would cause a crash. Also fixed an issue where property names with non-alphanumeric characters would crash. [#8785](https://github.com/CesiumGS/cesium/pull/8785)
 - Fixed a bug where `DebugCameraPrimitive` was ignoring the near and far planes of the `Camera`. [#8848](https://github.com/CesiumGS/cesium/issues/8848)
+- Fixed ground primitives in orthographic mode. [#5110](https://github.com/CesiumGS/cesium/issues/5110)
 - Fixed the depth plane in orthographic mode. This improves the quality of polylines and other primitives that are rendered near the horizon. [8858](https://github.com/CesiumGS/cesium/pull/8858)
 
 ### 1.69.0 - 2020-05-01
diff --git a/Source/Renderer/UniformState.js b/Source/Renderer/UniformState.js
index d456419789c0..a67ff401fdf1 100644
--- a/Source/Renderer/UniformState.js
+++ b/Source/Renderer/UniformState.js
@@ -1286,10 +1286,14 @@ UniformState.prototype.update = function (frameState) {
   var fov = camera.frustum.fov;
   var viewport = this._viewport;
   var pixelSizePerMeter;
-  if (viewport.height > viewport.width) {
-    pixelSizePerMeter = (Math.tan(0.5 * fov) * 2.0) / viewport.height;
+  if (defined(fov)) {
+    if (viewport.height > viewport.width) {
+      pixelSizePerMeter = (Math.tan(0.5 * fov) * 2.0) / viewport.height;
+    } else {
+      pixelSizePerMeter = (Math.tan(0.5 * fov) * 2.0) / viewport.width;
+    }
   } else {
-    pixelSizePerMeter = (Math.tan(0.5 * fov) * 2.0) / viewport.width;
+    pixelSizePerMeter = 1.0 / Math.max(viewport.width, viewport.height);
   }
 
   this._geometricToleranceOverMeter =
diff --git a/Source/Scene/ClassificationModel.js b/Source/Scene/ClassificationModel.js
index e9af83fcb4e4..679fa24cd0b0 100644
--- a/Source/Scene/ClassificationModel.js
+++ b/Source/Scene/ClassificationModel.js
@@ -628,7 +628,7 @@ function createProgram(model) {
     uniformDecl +
     "void main() {\n" +
     computePosition +
-    "    gl_Position = czm_depthClampFarPlane(positionInClipCoords);\n" +
+    "    gl_Position = czm_depthClamp(positionInClipCoords);\n" +
     "}\n";
   var fs =
     "#ifdef GL_EXT_frag_depth\n" +
@@ -637,7 +637,7 @@ function createProgram(model) {
     "void main() \n" +
     "{ \n" +
     "    gl_FragColor = vec4(1.0); \n" +
-    "    czm_writeDepthClampedToFarPlane();\n" +
+    "    czm_writeDepthClamp();\n" +
     "}\n";
 
   if (model.extensionsUsed.WEB3D_quantized_attributes) {
diff --git a/Source/Scene/Primitive.js b/Source/Scene/Primitive.js
index 16ce0c782d51..465362ea8836 100644
--- a/Source/Scene/Primitive.js
+++ b/Source/Scene/Primitive.js
@@ -1132,17 +1132,10 @@ function depthClampVS(vertexShaderSource) {
     vertexShaderSource,
     "czm_non_depth_clamp_main"
   );
-  // The varying should be surround by #ifdef GL_EXT_frag_depth as an optimization.
-  // It is not to workaround an issue with Edge:
-  //     https://developer.microsoft.com/en-us/microsoft-edge/platform/issues/12120362/
   modifiedVS +=
-    "varying float v_WindowZ;\n" +
     "void main() {\n" +
     "    czm_non_depth_clamp_main();\n" +
-    "    vec4 position = gl_Position;\n" +
-    "    v_WindowZ = (0.5 * (position.z / position.w) + 0.5) * position.w;\n" +
-    "    position.z = min(position.z, position.w);\n" +
-    "    gl_Position = position;\n" +
+    "    gl_Position = czm_depthClamp(gl_Position);" +
     "}\n";
   return modifiedVS;
 }
@@ -1153,14 +1146,13 @@ function depthClampFS(fragmentShaderSource) {
     "czm_non_depth_clamp_main"
   );
   modifiedFS +=
-    "varying float v_WindowZ;\n" +
     "void main() {\n" +
     "    czm_non_depth_clamp_main();\n" +
     "#if defined(GL_EXT_frag_depth)\n" +
     "    #if defined(LOG_DEPTH)\n" +
     "        czm_writeLogDepth();\n" +
     "    #else\n" +
-    "        gl_FragDepthEXT = min(v_WindowZ * gl_FragCoord.w, 1.0);\n" +
+    "        czm_writeDepthClamp();\n" +
     "    #endif\n" +
     "#endif\n" +
     "}\n";
diff --git a/Source/Shaders/Builtin/Functions/depthClamp.glsl b/Source/Shaders/Builtin/Functions/depthClamp.glsl
new file mode 100644
index 000000000000..f83356a1b56d
--- /dev/null
+++ b/Source/Shaders/Builtin/Functions/depthClamp.glsl
@@ -0,0 +1,27 @@
+// emulated noperspective
+#ifndef LOG_DEPTH
+varying float v_WindowZ;
+#endif
+
+/**
+ * Clamps a vertex to the near and far planes.
+ *
+ * @name czm_depthClamp
+ * @glslFunction
+ *
+ * @param {vec4} coords The vertex in clip coordinates.
+ * @returns {vec4} The vertex clipped to the near and far planes.
+ *
+ * @example
+ * gl_Position = czm_depthClamp(czm_modelViewProjection * vec4(position, 1.0));
+ *
+ * @see czm_writeDepthClamp
+ */
+vec4 czm_depthClamp(vec4 coords)
+{
+#ifndef LOG_DEPTH
+    v_WindowZ = (0.5 * (coords.z / coords.w) + 0.5) * coords.w;
+    coords.z = clamp(coords.z, -coords.w, +coords.w);
+#endif
+    return coords;
+}
diff --git a/Source/Shaders/Builtin/Functions/depthClampFarPlane.glsl b/Source/Shaders/Builtin/Functions/depthClampFarPlane.glsl
deleted file mode 100644
index bec295024033..000000000000
--- a/Source/Shaders/Builtin/Functions/depthClampFarPlane.glsl
+++ /dev/null
@@ -1,27 +0,0 @@
-// emulated noperspective
-#ifndef LOG_DEPTH
-varying float v_WindowZ;
-#endif
-
-/**
- * Clamps a vertex to the far plane.
- *
- * @name czm_depthClampFarPlane
- * @glslFunction
- *
- * @param {vec4} coords The vertex in clip coordinates.
- * @returns {vec4} The vertex clipped to the far plane.
- *
- * @example
- * gl_Position = czm_depthClampFarPlane(czm_modelViewProjection * vec4(position, 1.0));
- *
- * @see czm_writeDepthClampedToFarPlane
- */
-vec4 czm_depthClampFarPlane(vec4 coords)
-{
-#ifndef LOG_DEPTH
-    v_WindowZ = (0.5 * (coords.z / coords.w) + 0.5) * coords.w;
-    coords.z = min(coords.z, coords.w);
-#endif
-    return coords;
-}
diff --git a/Source/Shaders/Builtin/Functions/writeDepthClampedToFarPlane.glsl b/Source/Shaders/Builtin/Functions/writeDepthClamp.glsl
similarity index 62%
rename from Source/Shaders/Builtin/Functions/writeDepthClampedToFarPlane.glsl
rename to Source/Shaders/Builtin/Functions/writeDepthClamp.glsl
index bf8cf3209b45..9006fe0a1c99 100644
--- a/Source/Shaders/Builtin/Functions/writeDepthClampedToFarPlane.glsl
+++ b/Source/Shaders/Builtin/Functions/writeDepthClamp.glsl
@@ -8,18 +8,18 @@ varying float v_WindowZ;
  * The shader must enable the GL_EXT_frag_depth extension.
  * </p>
  *
- * @name czm_writeDepthClampedToFarPlane
+ * @name czm_writeDepthClamp
  * @glslFunction
  *
  * @example
  * gl_FragColor = color;
- * czm_writeDepthClampedToFarPlane();
+ * czm_writeDepthClamp();
  *
- * @see czm_depthClampFarPlane
+ * @see czm_depthClamp
  */
-void czm_writeDepthClampedToFarPlane()
+void czm_writeDepthClamp()
 {
 #if defined(GL_EXT_frag_depth) && !defined(LOG_DEPTH)
-    gl_FragDepthEXT = min(v_WindowZ * gl_FragCoord.w, 1.0);
+    gl_FragDepthEXT = clamp(v_WindowZ * gl_FragCoord.w, 0.0, 1.0);
 #endif
 }
diff --git a/Source/Shaders/PolylineShadowVolumeFS.glsl b/Source/Shaders/PolylineShadowVolumeFS.glsl
index d8b65a80fd0e..2ec1748e963d 100644
--- a/Source/Shaders/PolylineShadowVolumeFS.glsl
+++ b/Source/Shaders/PolylineShadowVolumeFS.glsl
@@ -83,5 +83,5 @@ void main(void)
     gl_FragColor = vec4(material.diffuse + material.emission, material.alpha);
 #endif // PER_INSTANCE_COLOR
 
-    czm_writeDepthClampedToFarPlane();
+    czm_writeDepthClamp();
 }
diff --git a/Source/Shaders/PolylineShadowVolumeVS.glsl b/Source/Shaders/PolylineShadowVolumeVS.glsl
index 9d17be9312d2..61c9f04ed625 100644
--- a/Source/Shaders/PolylineShadowVolumeVS.glsl
+++ b/Source/Shaders/PolylineShadowVolumeVS.glsl
@@ -157,7 +157,7 @@ void main()
 #endif
 
     positionEC.xyz += width * normalEC;
-    gl_Position = czm_depthClampFarPlane(czm_projection * positionEC);
+    gl_Position = czm_depthClamp(czm_projection * positionEC);
 
 #ifdef ANGLE_VARYING
     // Approximate relative screen space direction of the line.
diff --git a/Source/Shaders/ShadowVolumeAppearanceFS.glsl b/Source/Shaders/ShadowVolumeAppearanceFS.glsl
index 1231a8b0cbae..1b5de0d7eedc 100644
--- a/Source/Shaders/ShadowVolumeAppearanceFS.glsl
+++ b/Source/Shaders/ShadowVolumeAppearanceFS.glsl
@@ -73,7 +73,7 @@ void main(void)
 #ifdef CULL_FRAGMENTS
     if (0.0 <= uv.x && uv.x <= 1.0 && 0.0 <= uv.y && uv.y <= 1.0) {
         gl_FragColor.a = 1.0; // 0.0 alpha leads to discard from ShaderSource.createPickFragmentShaderSource
-        czm_writeDepthClampedToFarPlane();
+        czm_writeDepthClamp();
     }
 #else // CULL_FRAGMENTS
         gl_FragColor.a = 1.0;
@@ -147,6 +147,6 @@ void main(void)
 #endif // FLAT
 
 #endif // PER_INSTANCE_COLOR
-    czm_writeDepthClampedToFarPlane();
+    czm_writeDepthClamp();
 #endif // PICK
 }
diff --git a/Source/Shaders/ShadowVolumeAppearanceVS.glsl b/Source/Shaders/ShadowVolumeAppearanceVS.glsl
index 0f2b1c456a3b..8938a0447469 100644
--- a/Source/Shaders/ShadowVolumeAppearanceVS.glsl
+++ b/Source/Shaders/ShadowVolumeAppearanceVS.glsl
@@ -97,5 +97,5 @@ void main()
     v_color = czm_batchTable_color(batchId);
 #endif
 
-    gl_Position = czm_depthClampFarPlane(czm_modelViewProjectionRelativeToEye * position);
+    gl_Position = czm_depthClamp(czm_modelViewProjectionRelativeToEye * position);
 }
diff --git a/Source/Shaders/ShadowVolumeFS.glsl b/Source/Shaders/ShadowVolumeFS.glsl
index b1af3c3ff493..267d55b6fa87 100644
--- a/Source/Shaders/ShadowVolumeFS.glsl
+++ b/Source/Shaders/ShadowVolumeFS.glsl
@@ -13,5 +13,5 @@ void main(void)
 #else
     gl_FragColor = vec4(1.0);
 #endif
-    czm_writeDepthClampedToFarPlane();
+    czm_writeDepthClamp();
 }
diff --git a/Source/Shaders/VectorTileVS.glsl b/Source/Shaders/VectorTileVS.glsl
index 6c7a5278e8a3..179f3dc69be4 100644
--- a/Source/Shaders/VectorTileVS.glsl
+++ b/Source/Shaders/VectorTileVS.glsl
@@ -5,5 +5,5 @@ uniform mat4 u_modifiedModelViewProjection;
 
 void main()
 {
-    gl_Position = czm_depthClampFarPlane(u_modifiedModelViewProjection * vec4(position, 1.0));
+    gl_Position = czm_depthClamp(u_modifiedModelViewProjection * vec4(position, 1.0));
 }
diff --git a/Specs/Scene/ShadowVolumeAppearanceSpec.js b/Specs/Scene/ShadowVolumeAppearanceSpec.js
index fd5e69eff2a0..deba2c4feb9b 100644
--- a/Specs/Scene/ShadowVolumeAppearanceSpec.js
+++ b/Specs/Scene/ShadowVolumeAppearanceSpec.js
@@ -21,7 +21,7 @@ describe("Scene/ShadowVolumeAppearance", function () {
     "attribute float batchId;\n" +
     "void main() {\n" +
     "    vec4 position = czm_computePosition();\n" +
-    "    gl_Position = czm_depthClampFarPlane(czm_modelViewProjectionRelativeToEye * position);\n" +
+    "    gl_Position = czm_depthClamp(czm_modelViewProjectionRelativeToEye * position);\n" +
     "}\n";
 
   var unitSphereEllipsoid = Ellipsoid.UNIT_SPHERE;