GEE基础学习——Hillshade山阴的计算和显示

// Hillshade example.  This is a demonstration of computing
// a hillshade from terrain data and displaying multiple
// layers based on multiple view geometries.  Hillshade
// creation is also provided by ee.Terrain.hillshade().
// Define a function to convert from degrees to radians.

function radians(img) {

return img.toFloat().multiply(Math.PI).divide(180);

}
// Define a function to compute a hillshade from terrain data

// for the given sun azimuth and elevation.

function hillshade(az, ze, slope, aspect) {

// Convert angles to radians.

var azimuth = radians(ee.Image(az));

var zenith = radians(ee.Image(ze));

// Note that methods on images are needed to do the computation.

// i.e. JavaScript operators (e.g. +, -, /, *) do not work on images.

// The following implements:

// Hillshade = cos(Azimuth - Aspect) * sin(Slope) * sin(Zenith) +

//     cos(Zenith) * cos(Slope)

return azimuth.subtract(aspect).cos()

.multiply(slope.sin())

.multiply(zenith.sin())

.add(

zenith.cos().multiply(slope.cos()));

}
// Compute terrain meaasures from the SRTM DEM.

var terrain = ee.Algorithms.Terrain(ee.Image('CGIAR/SRTM90_V4'));

var slope = radians(terrain.select('slope'));

var aspect = radians(terrain.select('aspect'));
// For loops are needed for control-flow operations on client-side

// operations.  Here Map.addLayer() is a client operation that needs

// to be performed in a for loop.  In general, avoid for loops

// for any server-side operation.

Map.setCenter(-121.767, 46.852, 11);

for (var i = 0; i < 360; i += 60) {

Map.addLayer(hillshade(i, 60, slope, aspect), {}, i + ' deg');

}