ee.Image.reproject

Forcez le calcul d'une image dans une projection et une résolution données.

Utilisation	Renvoie
Image.reproject(crs, crsTransform, scale)	Image

Argument	Type	Détails
ceci : image	Image	Image à reprojeter.
crs	Projection	CRS dans lequel projeter l'image.
crsTransform	Liste, valeur par défaut : null	Liste des valeurs de transformation du CRS. Il s'agit d'un ordre de ligne principale de la matrice de transformation 3x2. Cette option est incompatible avec l'option de mise à l'échelle et remplace toute transformation déjà appliquée à la projection.
scale	Float, valeur par défaut : null	Si une échelle est spécifiée, la projection est mise à l'échelle en divisant la valeur d'échelle spécifiée par la taille nominale d'un mètre dans la projection spécifiée. Si l'échelle n'est pas spécifiée, celle de la projection donnée est utilisée.

Exemples

Éditeur de code (JavaScript)

// 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.
var dem1 = ee.Image('NASA/NASADEM_HGT/001').select('elevation');
var dem2 = ee.Image('CGIAR/SRTM90_V4').select('elevation');
var demMean = ee.ImageCollection([dem1, dem2]).mean();

// Display the DEMs on the map, note that they all render as expected.
var demVisParams = {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).
var demCompSlope = 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.
var slopeScale = 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.
var nasademProj = dem1.projection();
var demMeanReproj = demMean.reproject(nasademProj);
var slopeRefProj = 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.
var demMeanProj = ee.ImageCollection([dem1, dem2]).mean()
                      .setDefaultProjection(nasademProj);
var slopeProj = ee.Terrain.slope(demMeanProj);
Map.addLayer(slopeProj, {min: 0, max: 45}, 'slope w/ default projection set');

Configuration de Python

Consultez la page Environnement Python pour en savoir plus sur l'API Python et sur l'utilisation de geemap pour le développement interactif.

import ee
import geemap.core as geemap

Colab (Python)

# 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