![]() reduceResolution, for when you want to aggregate higher resolution.Var output = collection.reduce(.).reproject(proj) Ī few cases that require a fixed projection include: Some projection that is suitable for your area of interest. For example, to force a composite to be produced in a Using reproject() results in the inputsīeing requested in the projection specified in the reproject() call.Ĭomputations in your code before the reproject() call will be done You can force operations to be performed in a specific projection with the Projection can be forced by reprojecting the output as described in the following If the optimized display image somehow isn't sufficient, computation in a specific But it does mean that the output can appear different at In the vast majority of use cases, having no projection is not a problemĪnd is actually a valuable optimization, as it allows previewing the resultsĪt any zoom level without having to wait for the full resolution computation ![]() Output projection that accompanies the request that specified how to compute the ( learn more), and at that point, there's always an Information, but the pixels aren't actually computed until they're needed Users often find this behavior confusing and worry about the "lost" projection Gives this friendly reminder to provide a complete specification for the output. Generally, an aggregation at 1-degree scale is not desired or intended, so Earth Engine The default WGS84 projection is invalid for aggregations. If you try to use an image like this in a computation, you may see an error like: Var mosaic = collection.filterDate('', '').mosaic() Projection, which is WGS84 with 1-degree scale.įor example: Code Editor (JavaScript) var collection = ee.ImageCollection('LANDSAT/LC08/C02/T1_TOA') An image which is aĬomposite or mosaic of input images with different projections will have the default Reducing an ImageCollection containing images with different projections Require you to specify a projection and/or scale. Only for output that's ambiguous will Earth Engine Unless you need your computation to occur in a specific projection, there is generally Image.projection: The bands of the specified image contain different projections. With at least one band that doesn't have the same projection as the others, you may see an Because each band of an image can have aĭifferent scale and/or projection, if you call projection() on an image Native resolution is the nominal pixel scale in meters of the lowest level of the Note that by calling nominalScale() on the ee.Projection returnedīy projection(), you can determine the native resolution of the image. Print('Scale in meters:', image.projection().nominalScale()) Print('Projection, crs, and crs_transform:', image.projection()) Image by calling projection() on it: Code Editor (JavaScript) var image = ee.Image('LANDSAT/LC08/C02/T1_TOA/LC08_044034_20140318').select(0) In Earth Engine, projections are specified by a Coordinate Reference System (CRS or Reprojection: specifically, the output projection and scale. Curved lines indicate the flow of information to the Projections (left side of flow chart) of each operationĪre determined from the output. Flow chart of operations corresponding to the display of a MODIS That the inputs are requested in maps mercator, at a scale determined by the zoom level This projection propagates back through the sequence of operations such Maps mercator projection of the map display in theĬode Editor. That the projection of the input is determined by the output, specifically the The order of operations for this code sample is diagrammed in Figure 1. Map.addLayer(rescaled, visParams, 'Rescaled') Normalize the image and add it to the map. When youĭisplay images in the Code Editor, inputs are requested inįollowing simple operation on a MODIS image, which has aĬode Editor (JavaScript) // The input image has a SR-ORG:6974 (sinusoidal) projection. Mercator (EPSG:3857) projection), or with a reproject() call. The Map in the Code Editor (which has a maps The output may be determined from a function parameter (e.g. Specifically, inputs are requested in the output As with scale, the projection in which computations take place isĭetermined on a "pull" basis. Earth Engine is designed so that you rarely have to worry about map projections whenĭoing computations.
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