Pengumuman: Semua project nonkomersial yang terdaftar untuk menggunakan Earth Engine sebelum
15 April 2025 harus
memverifikasi kelayakan nonkomersial untuk mempertahankan akses Earth Engine.
Memetakan di atas ImageCollection
Tetap teratur dengan koleksi
Simpan dan kategorikan konten berdasarkan preferensi Anda.
Untuk menerapkan fungsi ke setiap Image dalam ImageCollection, gunakan
imageCollection.map(). Satu-satunya argumen untuk map() adalah
fungsi yang menggunakan satu parameter: ee.Image. Misalnya, kode berikut menambahkan band stempel waktu ke setiap gambar dalam koleksi.
Editor Kode (JavaScript)
// Load a Landsat 8 collection for a single path-row, 2021 images only.
var collection = ee.ImageCollection('LANDSAT/LC08/C02/T1_TOA')
.filterDate('2021', '2022')
.filter(ee.Filter.eq('WRS_PATH', 44))
.filter(ee.Filter.eq('WRS_ROW', 34));
// This function adds a band representing the image timestamp.
var addTime = function(image) {
return image.addBands(image.getNumber('system:time_start'));
};
// Map the function over the collection and display the result.
print(collection.map(addTime));
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 collection for a single path-row, 2021 images only.
collection = (
ee.ImageCollection('LANDSAT/LC08/C02/T1_TOA')
.filterDate('2021', '2022')
.filter(ee.Filter.eq('WRS_PATH', 44))
.filter(ee.Filter.eq('WRS_ROW', 34))
)
# This function adds a band representing the image timestamp.
def add_time(image):
return image.addBands(image.getNumber('system:time_start'))
# Map the function over the collection and display the result.
display(collection.map(add_time))
Perhatikan bahwa dalam fungsi standar, metode getNumber() digunakan
untuk membuat Image baru dari nilai numerik properti. Seperti yang dibahas di
bagian Mengurangi dan
Membuat Komposisi, memiliki rentang waktu berguna untuk pemodelan linear perubahan dan untuk membuat
komposit.
Fungsi yang dipetakan dibatasi dalam operasi yang dapat dilakukannya. Secara khusus, fungsi ini tidak dapat
mengubah variabel di luar fungsi; tidak dapat mencetak apa pun; tidak dapat menggunakan pernyataan 'if' atau 'for' JavaScript dan
Python. Namun, Anda dapat menggunakan ee.Algorithms.If() untuk
melakukan operasi kondisional dalam fungsi yang dipetakan. Contoh:
Editor Kode (JavaScript)
// Load a Landsat 8 collection for a single path-row, 2021 images only.
var collection = ee.ImageCollection('LANDSAT/LC08/C02/T1_TOA')
.filterDate('2021', '2022')
.filter(ee.Filter.eq('WRS_PATH', 44))
.filter(ee.Filter.eq('WRS_ROW', 34));
// This function uses a conditional statement to return the image if
// the solar elevation > 40 degrees. Otherwise it returns a "zero image".
var conditional = function(image) {
return ee.Algorithms.If(ee.Number(image.get('SUN_ELEVATION')).gt(40),
image,
ee.Image(0));
};
// Map the function over the collection and print the result. Expand the
// collection and note that 7 of the 22 images are now "zero images'.
print('Expand this to see the result', collection.map(conditional));
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 collection for a single path-row, 2021 images only.
collection = (
ee.ImageCollection('LANDSAT/LC08/C02/T1_TOA')
.filterDate('2021', '2022')
.filter(ee.Filter.eq('WRS_PATH', 44))
.filter(ee.Filter.eq('WRS_ROW', 34))
)
# This function uses a conditional statement to return the image if
# the solar elevation > 40 degrees. Otherwise it returns a "zero image".
def conditional(image):
return ee.Algorithms.If(
ee.Number(image.get('SUN_ELEVATION')).gt(40), image, ee.Image(0)
)
# Map the function over the collection and print the result. Expand the
# collection and note that 7 of the 22 images are now "zero images'.
display('Expand this to see the result', collection.map(conditional))
Periksa daftar gambar dalam ImageCollection output dan perhatikan bahwa saat
kondisi yang dievaluasi oleh algoritma If() bernilai benar, output akan berisi
gambar konstan. Meskipun ini menunjukkan fungsi bersyarat sisi server (pelajari lebih lanjut klien vs. server di Earth Engine), hindari If() secara umum dan gunakan filter.
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\u003eThe \u003ccode\u003eimageCollection.map()\u003c/code\u003e function applies a specified function to each image within an ImageCollection in Earth Engine.\u003c/p\u003e\n"],["\u003cp\u003eThe function passed to \u003ccode\u003emap()\u003c/code\u003e should accept a single \u003ccode\u003eee.Image\u003c/code\u003e as input and return a modified image.\u003c/p\u003e\n"],["\u003cp\u003eWhile mapped functions have limitations like not modifying external variables or using conventional loops, conditional operations are achievable using \u003ccode\u003eee.Algorithms.If()\u003c/code\u003e.\u003c/p\u003e\n"],["\u003cp\u003eDespite the availability of \u003ccode\u003eee.Algorithms.If()\u003c/code\u003e, prioritize using filters for conditional logic whenever possible for better efficiency and code clarity.\u003c/p\u003e\n"]]],["To apply a function to each `Image` in an `ImageCollection`, use `imageCollection.map()`, providing a function that takes an `ee.Image` as input. This function can add bands, such as a timestamp using `image.addBands(image.getNumber('system:time_start'))`. Conditional logic can be implemented within the mapped function using `ee.Algorithms.If()`, allowing for operations based on image properties like solar elevation, though filtering is preferred. This conditional process is server-side and operates on the entire collection.\n"],null,["# Mapping over an ImageCollection\n\nTo apply a function to every `Image` in an `ImageCollection` use\n`imageCollection.map()`. The only argument to `map()` is a\nfunction which takes one parameter: an `ee.Image`. For example, the following\ncode adds a timestamp band to every image in the collection.\n\n### Code Editor (JavaScript)\n\n```javascript\n// Load a Landsat 8 collection for a single path-row, 2021 images only.\nvar collection = ee.ImageCollection('LANDSAT/LC08/C02/T1_TOA')\n .filterDate('2021', '2022')\n .filter(ee.Filter.eq('WRS_PATH', 44))\n .filter(ee.Filter.eq('WRS_ROW', 34));\n\n// This function adds a band representing the image timestamp.\nvar addTime = function(image) {\n return image.addBands(image.getNumber('system:time_start'));\n};\n\n// Map the function over the collection and display the result.\nprint(collection.map(addTime));\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 collection for a single path-row, 2021 images only.\ncollection = (\n ee.ImageCollection('LANDSAT/LC08/C02/T1_TOA')\n .filterDate('2021', '2022')\n .filter(ee.Filter.eq('WRS_PATH', 44))\n .filter(ee.Filter.eq('WRS_ROW', 34))\n)\n\n\n# This function adds a band representing the image timestamp.\ndef add_time(image):\n return image.addBands(image.getNumber('system:time_start'))\n\n\n# Map the function over the collection and display the result.\ndisplay(collection.map(add_time))\n```\n\nNote that in the predefined function, the `getNumber()` method is used\nto create a new `Image` from the numerical value of a property. As discussed in\nthe [Reducing](/earth-engine/guides/ic_reducing) and\n[Compositing](/earth-engine/guides/ic_composite_mosaic)\nsections, having the time band is useful for linear modeling of change and for making\ncomposites.\n\nThe mapped function is limited in the operations it can perform. Specifically, it can't\nmodify variables outside the function; it can't print anything; it can't use JavaScript and\nPython 'if' or 'for' statements. However, you can use `ee.Algorithms.If()` to\nperform conditional operations in a mapped function. For example:\n\n### Code Editor (JavaScript)\n\n```javascript\n// Load a Landsat 8 collection for a single path-row, 2021 images only.\nvar collection = ee.ImageCollection('LANDSAT/LC08/C02/T1_TOA')\n .filterDate('2021', '2022')\n .filter(ee.Filter.eq('WRS_PATH', 44))\n .filter(ee.Filter.eq('WRS_ROW', 34));\n\n// This function uses a conditional statement to return the image if\n// the solar elevation \u003e 40 degrees. Otherwise it returns a \"zero image\".\nvar conditional = function(image) {\n return ee.Algorithms.If(ee.Number(image.get('SUN_ELEVATION')).gt(40),\n image,\n ee.Image(0));\n};\n\n// Map the function over the collection and print the result. Expand the\n// collection and note that 7 of the 22 images are now \"zero images'.\nprint('Expand this to see the result', collection.map(conditional));\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 collection for a single path-row, 2021 images only.\ncollection = (\n ee.ImageCollection('LANDSAT/LC08/C02/T1_TOA')\n .filterDate('2021', '2022')\n .filter(ee.Filter.eq('WRS_PATH', 44))\n .filter(ee.Filter.eq('WRS_ROW', 34))\n)\n\n\n# This function uses a conditional statement to return the image if\n# the solar elevation \u003e 40 degrees. Otherwise it returns a \"zero image\".\ndef conditional(image):\n return ee.Algorithms.If(\n ee.Number(image.get('SUN_ELEVATION')).gt(40), image, ee.Image(0)\n )\n\n\n# Map the function over the collection and print the result. Expand the\n# collection and note that 7 of the 22 images are now \"zero images'.\ndisplay('Expand this to see the result', collection.map(conditional))\n```\n\nInspect the list of images in the output ImageCollection and note that when the\ncondition evaluated by the `If()` algorithm is true, the output contains a\nconstant image. Although this demonstrates a server-side conditional function\n([learn more about client vs. server in Earth Engine](/earth-engine/guides/client_server)),\navoid `If()` in general and use filters instead."]]
