For the best performance in Cesium, we implemented wind vectors using Cesium’s PolylineCollection instead of KML, thereby improving rendering speed. We were able to preserve nearly all of our KML file formats except for the wind vector products. The migration from Google Earth to Cesium was mostly smooth. All the image overlays and vector products were represented using KML files. The RapidScat portal was originally designed using Google Earth. The subsetting tool works with either the RapidScat or the ASCAT wind products. The portal will generate a wind map with the data in the selected area and put together a tarball of the original data for users to download. The RapidScat portal allows users to select a subset of data by using a rectangular subsetting tool. ![]() We have archived the scatterometer data since November 2014, and the archived data can be viewed via a calendar-controlled menu panel. The wind vectors and wind speed are separate layers that can be viewed together or separately. All the image data can be overlaid on top of each other with transparency control. To facilitate the understanding of the relationships between wind and rain, the portal also includes precipitation measurements from two microwave instruments, GMI (the Global Precipitation Microwave Imager) and AMSR2 (Advanced Microwave Scanning Radiometer). To provide a comprehensive depiction of the ocean surface winds, the portal includes near real-time wind measurement from another instrument: the European Advanced Scatterometer ( ASCAT). mandToExecute = new Cesium.The portal has a special focus on tropical storm monitoring therefore, it also includes the real-time storm tracks (updated at every 6 hours) and NOAA hurricane forecast tracks from multiple models. Var pass = // if you want the command to be executed in other pass, set it to corresponding value Var renderState = new Cesium.RenderState(parameters) Var framebuffer = new Cesium.Framebuffer(parameters) Var shaderProgram = new Cesium.ShaderProgram(parameters) Var modelMatrix = new Cesium.Matrix4(parameters) value can be a number, Cesium Cartesian vector, or Cesium.Texture return the value corresponding to the name in the function ![]() Var primitiveType = // you can set it to other values Var vertexArray = new Cesium.VertexArray(parameters) or you can take my wind visualization code as a example () so you may want to read the source code of Cesium to figure out how to initialize the below components, most of the APIs in the renderer module are private, Below is a fully commented example of how to create a primitive and add it to the scene with a custom draw command. The final step is to add the CustomPrimitive that contains the custom DrawCommand to the PrimitiveCollection of Scene. Fortunately, Cesium already provides the rendering to texture function-all I needed to do was simply pass my fragment shader code to Cesium.ComputeCommand and use Cesium.ComputeEngine to perform the GPGPU. The update method will be called before the start of each rendering.Īs for the computation on GPU (also known as GPGPU), by using the technique of rendering to texture, it is similar to doing custom rendering just use a fullscreen quad as vertex shader and write the calculation code in the fragment shader. It does not need to implement all the methods of Cesium.Primitive, only the update, isDestroyed, and the destroy method are necessary. To inject the DrawCommand into the render engine, a custom primitive object is needed. To build a DrawCommand, first initialize its components, which are ShaderProgram, Texture, Uniforms, and Framebuffer, piece by piece, and then combine them together to create a DrawCommand object. To perform custom rendering, a custom DrawCommand is required. The Cesium.DrawCommand contains everything needed in rendering, for example, Cesium.Framebuffer, Cesium.Texture, and Cesium.ShaderProgram. ![]() In Cesium, the key object of the rendering procedure is Cesium.DrawCommand: it is created in Cesium.Primitive, dispatched by Cesium.Scene, and executed in the render engine. For better performance, I needed to move the computation to the GPU, but I still had to render the trails, which meant working with the low level Cesium Renderer module. After some investigation, I realized that the Entity API performs computation on the CPU, and the computation for more than 10,000 particles is just too much for my CPU. At first I tried the Entity API to draw the particle trails, but the performance was not satisfying when I placed more than 10,000 particles.
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