// Use of ee.Image.reproject is rarely needed and should generally be avoided.// Defining the projection and scale of analysis should be handled by "scale",// "crs", and "crsTransform" parameters whenever they are offered by a function.// It is occasionally useful for forcing computation or visualization at a// desired scale and projection when alternative methods are not available. In// this example it is used to compute and visualize terrain slope from a DEM// composite.// Calculate mean elevation from two DEM datasets. The resulting composite// image has a default CRS of WGS84 with 1 degree pixels.vardem1=ee.Image('NASA/NASADEM_HGT/001').select('elevation');vardem2=ee.Image('CGIAR/SRTM90_V4').select('elevation');vardemMean=ee.ImageCollection([dem1,dem2]).mean();// Display the DEMs on the map, note that they all render as expected.vardemVisParams={min:500,max:2500};Map.setCenter(-123.457,47.815,11);Map.addLayer(dem1,demVisParams,'DEM 1');Map.addLayer(dem2,demVisParams,'DEM 2');Map.addLayer(demMean,demVisParams,'DEM composite');// Calculate terrain slope from the composite DEM (WGS84, 1 degree pixel scale).vardemCompSlope=ee.Terrain.slope(demMean);// Because the composite has 1 degree pixel scale, the slope calculation// is essenstially meaningless and difficult to even display (you may need to// zoom out to see the individual 1 degree pixels).Map.addLayer(demCompSlope,{min:0,max:0.3},'Slope');// We can use ee.Image.reproject to force the slope calculation and display// the result with a reasonable scale of 30 m on WGS84 CRS, for example.varslopeScale=ee.Terrain.slope(demMean.reproject({crs:'EPSG:4326',scale:30}));Map.addLayer(slopeScale,{min:0,max:45},'Slope w/ CRS and scale');// To more precisely control the reprojection, you can use the "crsTransform"// parameter instead of the "scale" parameter or set the projection according to// a reference image. For example, here the input composite image for the slope// function is set to match the grid spacing and alignment of the NASADEM image.varnasademProj=dem1.projection();vardemMeanReproj=demMean.reproject(nasademProj);varslopeRefProj=ee.Terrain.slope(demMeanReproj);Map.addLayer(slopeRefProj,{min:0,max:45},'Slope w/ reference proj');print('Reference projection',nasademProj);print('DEM composite projection',demMeanReproj.projection());// An alternative method for changing the projection of image composites// (not accepting the default WGS84 CRS with 1 degree pixel scale) is to// explicitly set the default projection using ee.Image.setDefaultProjection,// which will not force resampling, like ee.Image.reproject will.vardemMeanProj=ee.ImageCollection([dem1,dem2]).mean().setDefaultProjection(nasademProj);varslopeProj=ee.Terrain.slope(demMeanProj);Map.addLayer(slopeProj,{min:0,max:45},'slope w/ default projection set');

# Use of ee.Image.reproject is rarely needed and should generally be avoided.# Defining the projection and scale of analysis should be handled by "scale",# "crs", and "crsTransform" parameters whenever they are offered by a function.# It is occasionally useful for forcing computation or visualization at a# desired scale and projection when alternative methods are not available. In# this example it is used to compute and visualize terrain slope from a DEM# composite.# Calculate mean elevation from two DEM datasets. The resulting composite# image has a default CRS of WGS84 with 1 degree pixels.dem_1=ee.Image('NASA/NASADEM_HGT/001').select('elevation')dem_2=ee.Image('CGIAR/SRTM90_V4').select('elevation')dem_mean=ee.ImageCollection([dem_1,dem_2]).mean()# Display the DEMs on the map, note that they all render as expected.dem_vis_params={'min':500,'max':2500}m=geemap.Map()m.set_center(-123.457,47.815,11)m.add_layer(dem_1,dem_vis_params,'DEM 1')m.add_layer(dem_2,dem_vis_params,'DEM 2')m.add_layer(dem_mean,dem_vis_params,'DEM composite')# Calculate terrain slope from the composite DEM (WGS84, 1 degree pixel scale).dem_comp_slope=ee.Terrain.slope(dem_mean)# Because the composite has 1 degree pixel scale, the slope calculation# is essenstially meaningless and difficult to even display (you may need to# zoom out to see the individual 1 degree pixels).m.add_layer(dem_comp_slope,{'min':0,'max':0.3},'Slope')# We can use ee.Image.reproject to force the slope calculation and display# the result with a reasonable scale of 30 m on WGS84 CRS, for example.slope_scale=ee.Terrain.slope(dem_mean.reproject(crs='EPSG:4326',scale=30))m.add_layer(slope_scale,{'min':0,'max':45},'Slope w/ CRS and scale')# To more precisely control the reprojection, you can use the "crsTransform"# parameter instead of the "scale" parameter or set the projection according to# a reference image. For example, here the input composite image for the slope# function is set to match the grid spacing and alignment of the NASADEM image.nasadem_proj=dem_1.projection()dem_mean_reproj=dem_mean.reproject(nasadem_proj)slope_ref_proj=ee.Terrain.slope(dem_mean_reproj)m.add_layer(slope_ref_proj,{'min':0,'max':45},'Slope w/ reference proj')display('Reference projection',nasadem_proj)display('DEM composite projection',dem_mean_reproj.projection())# An alternative method for changing the projection of image composites# (not accepting the default WGS84 CRS with 1 degree pixel scale) is to# explicitly set the default projection using ee.Image.setDefaultProjection,# which will not force resampling, like ee.Image.reproject will.dem_mean_proj=(ee.ImageCollection([dem_1,dem_2]).mean().setDefaultProjection(nasadem_proj))slope_proj=ee.Terrain.slope(dem_mean_proj)m.add_layer(slope_proj,{'min':0,'max':45},'slope w/ default projection set')m