Pengumuman: Semua project nonkomersial yang terdaftar untuk menggunakan Earth Engine sebelum
15 April 2025 harus
memverifikasi kelayakan nonkomersial untuk mempertahankan akses Earth Engine.
Operasi Matematika
Tetap teratur dengan koleksi
Simpan dan kategorikan konten berdasarkan preferensi Anda.
Matematika gambar dapat dilakukan menggunakan operator seperti add() dan
subtract(), tetapi untuk komputasi kompleks dengan lebih dari beberapa istilah, fungsi expression() memberikan alternatif yang baik. Lihat bagian berikut untuk mengetahui informasi selengkapnya tentang operator dan ekspresi.
Operator
Operator matematika melakukan operasi aritmatika dasar pada band gambar. Fungsi ini memerlukan dua input:
dua gambar atau satu gambar dan istilah konstan, yang
ditafsirkan sebagai gambar konstan satu band tanpa piksel yang disamarkan. Operasi dilakukan
per piksel untuk setiap band.
Sebagai contoh dasar, pertimbangkan tugas menghitung Normalized Difference Vegetation
Index (NDVI) menggunakan citra VIIRS, dengan operator add(), subtract(),
dan divide() digunakan:
Editor Kode (JavaScript)
// Load a VIIRS 8-day surface reflectance composite for May 2024.
var viirs202405 = ee.ImageCollection('NASA/VIIRS/002/VNP09H1').filter(
ee.Filter.date('2024-05-01', '2024-05-16')).first();
// Compute NDVI.
var ndvi202405 = viirs202405.select('SurfReflect_I2')
.subtract(viirs202405.select('SurfReflect_I1'))
.divide(viirs202405.select('SurfReflect_I2')
.add(viirs202405.select('SurfReflect_I1')));
Penyiapan Python
Lihat halaman
Lingkungan Python untuk mengetahui informasi tentang Python API dan penggunaan
geemap untuk pengembangan interaktif.
import ee
import geemap.core as geemap
Colab (Python)
# Load a VIIRS 8-day surface reflectance composite for May 2024.
viirs202405 = (
ee.ImageCollection('NASA/VIIRS/002/VNP09H1')
.filter(ee.Filter.date('2024-05-01', '2024-05-16'))
.first()
)
# Compute NDVI.
ndvi202405 = (
viirs202405.select('SurfReflect_I2')
.subtract(viirs202405.select('SurfReflect_I1'))
.divide(
viirs202405.select('SurfReflect_I2').add(
viirs202405.select('SurfReflect_I1')
)
)
)
Hanya persimpangan piksel yang tidak disamarkan di antara dua input yang
dipertimbangkan dan ditampilkan sebagai tidak disamarkan, yang lainnya akan disamarkan. Secara umum, jika salah satu input hanya memiliki
satu band, input tersebut akan digunakan terhadap semua band di input lainnya. Jika input memiliki jumlah
band yang sama, tetapi tidak memiliki nama yang sama, input tersebut akan digunakan secara berpasangan dalam urutan alami. Band
output diberi nama untuk input yang lebih panjang dari dua input, atau jika panjangnya sama, dalam
urutan input pertama. Jenis piksel output adalah gabungan dari jenis input.
Contoh pengurangan gambar multi-band berikut menunjukkan cara band dicocokkan secara otomatis, sehingga menghasilkan "vektor perubahan" untuk setiap piksel untuk setiap band yang terjadi bersama.
Editor Kode (JavaScript)
// Load a VIIRS 8-day surface reflectance composite for September 2024.
var viirs202409 = ee.ImageCollection('NASA/VIIRS/002/VNP09H1').filter(
ee.Filter.date('2024-09-01', '2024-09-16')).first();
// Compute multi-band difference between the September composite and the
// previously loaded May composite.
var diff = viirs202409.subtract(ndvi202405);
Map.addLayer(diff, {
bands: ['SurfReflect_I1', 'SurfReflect_I2', 'SurfReflect_I3'],
min: -1,
max: 1
}, 'difference');
// Compute the squared difference in each band.
var squaredDifference = diff.pow(2);
Map.addLayer(squaredDifference, {
bands: ['SurfReflect_I1', 'SurfReflect_I2', 'SurfReflect_I3'],
min: 0,
max: 0.7
}, 'squared diff.');
Penyiapan Python
Lihat halaman
Lingkungan Python untuk mengetahui informasi tentang Python API dan penggunaan
geemap untuk pengembangan interaktif.
import ee
import geemap.core as geemap
Colab (Python)
# Load a VIIRS 8-day surface reflectance composite for September 2024.
viirs202409 = (
ee.ImageCollection('NASA/VIIRS/002/VNP09H1')
.filter(ee.Filter.date('2024-09-01', '2024-09-16'))
.first()
)
# Compute multi-band difference between the September composite and the
# previously loaded May composite.
diff = viirs202409.subtract(ndvi202405)
m = geemap.Map()
m.add_layer(
diff,
{
'bands': ['SurfReflect_I1', 'SurfReflect_I2', 'SurfReflect_I3'],
'min': -1,
'max': 1,
},
'difference',
)
# Compute the squared difference in each band.
squared_difference = diff.pow(2)
m.add_layer(
squared_difference,
{
'bands': ['SurfReflect_I1', 'SurfReflect_I2', 'SurfReflect_I3'],
'min': 0,
'max': 0.7,
},
'squared diff.',
)
display(m)
Di bagian kedua contoh ini, perbedaan kuadrat dihitung menggunakan
image.pow(2). Untuk mengetahui daftar lengkap operator matematika yang menangani
aritmetika dasar, trigonometri, eksponensial, pembulatan, casting, operasi bitwise,
dan lainnya, lihat dokumentasi API.
Ekspresi
Untuk menerapkan ekspresi matematika yang lebih kompleks, pertimbangkan untuk menggunakan
image.expression(), yang mengurai representasi teks dari operasi matematika.
Contoh berikut menggunakan expression() untuk menghitung Enhanced Vegetation Index (EVI):
Editor Kode (JavaScript)
// Load a Landsat 8 image.
var image = ee.Image('LANDSAT/LC08/C02/T1_TOA/LC08_044034_20140318');
// Compute the EVI using an expression.
var evi = image.expression(
'2.5 * ((NIR - RED) / (NIR + 6 * RED - 7.5 * BLUE + 1))', {
'NIR': image.select('B5'),
'RED': image.select('B4'),
'BLUE': image.select('B2')
});
Map.centerObject(image, 9);
Map.addLayer(evi, {min: -1, max: 1, palette: ['a6611a', 'f5f5f5', '4dac26']});
Penyiapan Python
Lihat halaman
Lingkungan Python untuk mengetahui informasi tentang Python API dan penggunaan
geemap untuk pengembangan interaktif.
import ee
import geemap.core as geemap
Colab (Python)
# Load a Landsat 8 image.
image = ee.Image('LANDSAT/LC08/C02/T1_TOA/LC08_044034_20140318')
# Compute the EVI using an expression.
evi = image.expression(
'2.5 * ((NIR - RED) / (NIR + 6 * RED - 7.5 * BLUE + 1))',
{
'NIR': image.select('B5'),
'RED': image.select('B4'),
'BLUE': image.select('B2'),
},
)
# Define a map centered on San Francisco Bay.
map_evi = geemap.Map(center=[37.4675, -122.1363], zoom=9)
# Add the image layer to the map and display it.
map_evi.add_layer(
evi, {'min': -1, 'max': 1, 'palette': ['a6611a', 'f5f5f5', '4dac26']}, 'evi'
)
display(map_evi)
Perhatikan bahwa argumen pertama ke expression() adalah representasi tekstual dari
operasi matematika, argumen kedua adalah kamus dengan kunci adalah nama variabel yang digunakan
dalam ekspresi dan nilainya adalah band gambar tempat variabel harus
dipetakan. Band dalam gambar dapat disebut sebagai b("band name") atau
b(index), misalnya b(0), bukan
menyediakan kamus. Band dapat ditentukan dari gambar selain input saat menggunakan
kamus peta band. Perhatikan bahwa expression() menggunakan "pembagian lantai", yang membuang sisanya dan menampilkan bilangan bulat saat dua bilangan bulat dibagi. Misalnya
10 / 20 = 0. Untuk mengubah perilaku ini, kalikan salah satu operand dengan
1.0: 10 * 1.0 / 20 = 0.5. Hanya persimpangan piksel yang tidak disamarkan
yang dipertimbangkan dan ditampilkan sebagai tidak disamarkan saat band dari lebih dari satu gambar sumber
dievaluasi. Operator ekspresi yang didukung tercantum dalam tabel berikut.
Operator untuk expression()
| Jenis |
Simbol |
Nama |
| Aritmetika |
+ - * / % ** |
Tambahkan, Kurangi, Kalikan, Bagi, Modulus, Eksponen |
| Relasional |
== != < > <= >= |
Sama dengan, Tidak Sama dengan, Kurang dari, Lebih besar dari, dll. |
| Logis |
&& || ! ^ |
And, Or, Not, Xor |
| Ternary |
? : |
If then else |
Kecuali dinyatakan lain, konten di halaman ini dilisensikan berdasarkan Lisensi Creative Commons Attribution 4.0, sedangkan contoh kode dilisensikan berdasarkan Lisensi Apache 2.0. Untuk mengetahui informasi selengkapnya, lihat Kebijakan Situs Google Developers. Java adalah merek dagang terdaftar dari Oracle dan/atau afiliasinya.
Terakhir diperbarui pada 2025-07-25 UTC.
[null,null,["Terakhir diperbarui pada 2025-07-25 UTC."],[[["\u003cp\u003eEarth Engine provides tools for performing image math, including operators for basic arithmetic and the \u003ccode\u003eexpression()\u003c/code\u003e function for complex computations.\u003c/p\u003e\n"],["\u003cp\u003eOperators like \u003ccode\u003eadd()\u003c/code\u003e, \u003ccode\u003esubtract()\u003c/code\u003e, and \u003ccode\u003edivide()\u003c/code\u003e enable pixel-wise calculations between images or an image and a constant.\u003c/p\u003e\n"],["\u003cp\u003eThe \u003ccode\u003eexpression()\u003c/code\u003e function allows implementing custom formulas by parsing text representations of mathematical operations and mapping variables to image bands.\u003c/p\u003e\n"],["\u003cp\u003eWhen using \u003ccode\u003eexpression()\u003c/code\u003e, ensure to handle integer division appropriately by multiplying one operand by \u003ccode\u003e1.0\u003c/code\u003e to preserve decimal values if needed.\u003c/p\u003e\n"],["\u003cp\u003eBoth operators and expressions automatically handle band matching and masking, considering only unmasked pixels in the calculations.\u003c/p\u003e\n"]]],[],null,["# Mathematical Operations\n\n|---------------------------------------------------------------------------------------------------------------------------------------------------|-------------------------------------------------------------------------------------------------------------------------------|\n| [Run in Google Colab](https://colab.research.google.com/github/google/earthengine-community/blob/master/guides/linked/generated/image_math.ipynb) | [View source on GitHub](https://github.com/google/earthengine-community/blob/master/guides/linked/generated/image_math.ipynb) |\n\nImage math can be performed using operators like `add()` and\n`subtract()`, but for complex computations with more than a couple of terms, the\n`expression()` function provides a good alternative. See the following sections\nfor more information on [operators](#operators) and\n[expressions](#expressions).\n\nOperators\n---------\n\nMath operators perform basic arithmetic operations on image bands. They take two inputs:\neither two images or one image and a constant term, which\nis interpreted as a single-band constant image with no masked pixels. Operations are performed\nper pixel for each band.\n\nAs a basic example, consider the task of calculating the Normalized Difference Vegetation\nIndex (NDVI) using VIIRS imagery, where `add()`, `subtract()`,\nand `divide()` operators are used:\n\n### Code Editor (JavaScript)\n\n```javascript\n// Load a VIIRS 8-day surface reflectance composite for May 2024.\nvar viirs202405 = ee.ImageCollection('NASA/VIIRS/002/VNP09H1').filter(\n ee.Filter.date('2024-05-01', '2024-05-16')).first();\n\n// Compute NDVI.\nvar ndvi202405 = viirs202405.select('SurfReflect_I2')\n .subtract(viirs202405.select('SurfReflect_I1'))\n .divide(viirs202405.select('SurfReflect_I2')\n .add(viirs202405.select('SurfReflect_I1')));\n```\nPython setup\n\nSee the [Python Environment](/earth-engine/guides/python_install) page for information on the Python API and using\n`geemap` for interactive development. \n\n```python\nimport ee\nimport geemap.core as geemap\n```\n\n### Colab (Python)\n\n```python\n# Load a VIIRS 8-day surface reflectance composite for May 2024.\nviirs202405 = (\n ee.ImageCollection('NASA/VIIRS/002/VNP09H1')\n .filter(ee.Filter.date('2024-05-01', '2024-05-16'))\n .first()\n)\n\n# Compute NDVI.\nndvi202405 = (\n viirs202405.select('SurfReflect_I2')\n .subtract(viirs202405.select('SurfReflect_I1'))\n .divide(\n viirs202405.select('SurfReflect_I2').add(\n viirs202405.select('SurfReflect_I1')\n )\n )\n)\n```\n| **Note:** the normalized difference operation is available as a shortcut method: [`normalizedDifference()`](/earth-engine/apidocs/ee-image-normalizeddifference).\n\nOnly the intersection of unmasked pixels between the two inputs are\nconsidered and returned as unmasked, all else are masked. In general, if either input has only\none band, then it is used against all the bands in the other input. If the inputs have the same\nnumber of bands, but not the same names, they're used pairwise in the natural order. The\noutput bands are named for the longer of the two inputs, or if they're equal in length, in the\nfirst input's order. The type of the output pixels is the union of the input types.\n\nThe following example of multi-band image subtraction demonstrates how bands are matched\nautomatically, resulting in a \"change vector\" for each pixel for each co-occurring band.\n\n### Code Editor (JavaScript)\n\n```javascript\n// Load a VIIRS 8-day surface reflectance composite for September 2024.\nvar viirs202409 = ee.ImageCollection('NASA/VIIRS/002/VNP09H1').filter(\n ee.Filter.date('2024-09-01', '2024-09-16')).first();\n\n// Compute multi-band difference between the September composite and the\n// previously loaded May composite.\nvar diff = viirs202409.subtract(ndvi202405);\nMap.addLayer(diff, {\n bands: ['SurfReflect_I1', 'SurfReflect_I2', 'SurfReflect_I3'],\n min: -1,\n max: 1\n}, 'difference');\n\n// Compute the squared difference in each band.\nvar squaredDifference = diff.pow(2);\nMap.addLayer(squaredDifference, {\n bands: ['SurfReflect_I1', 'SurfReflect_I2', 'SurfReflect_I3'],\n min: 0,\n max: 0.7\n}, 'squared diff.');\n```\nPython setup\n\nSee the [Python Environment](/earth-engine/guides/python_install) page for information on the Python API and using\n`geemap` for interactive development. \n\n```python\nimport ee\nimport geemap.core as geemap\n```\n\n### Colab (Python)\n\n```python\n# Load a VIIRS 8-day surface reflectance composite for September 2024.\nviirs202409 = (\n ee.ImageCollection('NASA/VIIRS/002/VNP09H1')\n .filter(ee.Filter.date('2024-09-01', '2024-09-16'))\n .first()\n)\n\n# Compute multi-band difference between the September composite and the\n# previously loaded May composite.\ndiff = viirs202409.subtract(ndvi202405)\n\nm = geemap.Map()\nm.add_layer(\n diff,\n {\n 'bands': ['SurfReflect_I1', 'SurfReflect_I2', 'SurfReflect_I3'],\n 'min': -1,\n 'max': 1,\n },\n 'difference',\n)\n\n# Compute the squared difference in each band.\nsquared_difference = diff.pow(2)\n\nm.add_layer(\n squared_difference,\n {\n 'bands': ['SurfReflect_I1', 'SurfReflect_I2', 'SurfReflect_I3'],\n 'min': 0,\n 'max': 0.7,\n },\n 'squared diff.',\n)\ndisplay(m)\n```\n\nIn the second part of this example, the squared difference is computed using\n`image.pow(2)`. For the complete list of mathematical operators handling\nbasic arithmetic, trigonometry, exponentiation, rounding, casting, bitwise operations\nand more, see the [API documentation](/earth-engine/apidocs).\n\nExpressions\n-----------\n\nTo implement more complex mathematical expressions, consider using\n`image.expression()`, which parses a text representation of a math operation.\nThe following example uses `expression()` to compute the Enhanced\nVegetation Index (EVI):\n\n### Code Editor (JavaScript)\n\n```javascript\n// Load a Landsat 8 image.\nvar image = ee.Image('LANDSAT/LC08/C02/T1_TOA/LC08_044034_20140318');\n\n// Compute the EVI using an expression.\nvar evi = image.expression(\n '2.5 * ((NIR - RED) / (NIR + 6 * RED - 7.5 * BLUE + 1))', {\n 'NIR': image.select('B5'),\n 'RED': image.select('B4'),\n 'BLUE': image.select('B2')\n});\n\nMap.centerObject(image, 9);\nMap.addLayer(evi, {min: -1, max: 1, palette: ['a6611a', 'f5f5f5', '4dac26']});\n```\nPython setup\n\nSee the [Python Environment](/earth-engine/guides/python_install) page for information on the Python API and using\n`geemap` for interactive development. \n\n```python\nimport ee\nimport geemap.core as geemap\n```\n\n### Colab (Python)\n\n```python\n# Load a Landsat 8 image.\nimage = ee.Image('LANDSAT/LC08/C02/T1_TOA/LC08_044034_20140318')\n\n# Compute the EVI using an expression.\nevi = image.expression(\n '2.5 * ((NIR - RED) / (NIR + 6 * RED - 7.5 * BLUE + 1))',\n {\n 'NIR': image.select('B5'),\n 'RED': image.select('B4'),\n 'BLUE': image.select('B2'),\n },\n)\n\n# Define a map centered on San Francisco Bay.\nmap_evi = geemap.Map(center=[37.4675, -122.1363], zoom=9)\n\n# Add the image layer to the map and display it.\nmap_evi.add_layer(\n evi, {'min': -1, 'max': 1, 'palette': ['a6611a', 'f5f5f5', '4dac26']}, 'evi'\n)\ndisplay(map_evi)\n```\n\nObserve that the first argument to `expression()` is the textual representation of\nthe math operation, the second argument is a dictionary where the keys are variable names used\nin the expression and the values are the image bands to which the variables should be\nmapped. Bands in the image may be referred to as `b(\"band name\")` or\n`b(index)`, for example `b(0)`, instead\nof providing the dictionary. Bands can be defined from images other than the input when using\nthe band map dictionary. Note that `expression()` uses \"floor division\", which\ndiscards the remainder and returns an integer when two integers are divided. For example\n`10 / 20 = 0`. To change this behavior, multiply one of the operands by\n`1.0`: `10 * 1.0 / 20 = 0.5`. Only the intersection of unmasked pixels\nare considered and returned as unmasked when bands from more than one source image are\nevaluated. Supported expression operators are listed in the following table.\n\n| Type | Symbol | Name |\n|----------------|---------------------|----------------------------------------------------|\n| **Arithmetic** | + - \\* / % \\*\\* | Add, Subtract, Multiply, Divide, Modulus, Exponent |\n| **Relational** | == != \\\u003c \\\u003e \\\u003c= \\\u003e= | Equal, Not Equal, Less Than, Greater than, etc. |\n| **Logical** | \\&\\& \\|\\| ! \\^ | And, Or, Not, Xor |\n| **Ternary** | ? : | If then else |\n[Operators for `expression()`]"]]
Jalankan di Google Colab
Lihat sumber di GitHub