Google Earth Engine – Extracting Information from Image by Row and Column

google-earth-engine

I would like to iterate over an image in Google Earth Engine, but not sure how to reference the location in an image by row and column. Here is some example code:

var ROI = ee.Geometry.Rectangle(-82.5574, 35.5958, -82.5563, 35.59515); // define area

var collection = ee.ImageCollection('LANDSAT/LC08/C01/T1')
    .filterDate('2014-05-01', '2015-10-01')
    .filterBounds(ROI)
    .limit(1);

var composite = ee.Algorithms.Landsat.simpleComposite(collection);
var image = composite.clip(ROI);

Map.centerObject(ROI);
Map.addLayer(composite, {bands: 'B4,B3,B2', min:0, max:100}, "composite", false);
Map.addLayer(image, {bands: 'B4,B3,B2', min:0, max:100},"image");

// Extract projection information from the first band of a sample image in the collection.
var sample = ee.Image(collection.first());
var projection = sample.select('B1').projection();

// Reproject the composite image to the selected projection.
image = composite.reproject(projection).clip(ROI);

// Return the image metadata to the client.
var image_info = image.getInfo();

// On the clientside, using Javascript, print out the dimensions.
print('band B1 dimensions: ' + image_info.bands[0].dimensions);

print('image information', image);

The resulting image is 3 by 4. How can I reference the values at, say, position [0,0] or [1,3]?

I have tried using regular javascript syntax image[0][0], to no avail.

Best Answer

Earth Engine API does not provide a very friendly API to reference image pixels directly because this is not needed for most applications. But I can imagine situations where analyzing images pixel by pixel in their native projection may be required. Here is a quick addition to your script showing how to get pixel center and values: https://code.earthengine.google.com/7417ead66dc131af4e3378f6672738f9. Currently, the script will fail for large images but can be used for smaller images like in your example.

var ImageView = require('users/gena/packages:image-view').ImageView

var view = new ImageView(image)

print('Image dimensions: ', view.getDimensions())

Map.addLayer(view.getPixelCenters(), {}, 'pixel centers')
Map.addLayer(view.getPixelCenter(0, 0), {color: 'red'}, '(0, 0)')
Map.addLayer(view.getPixelCenter(3, 2), {color: 'yellow'}, '(2, 3)')

print('(0, 0) pixel value: ', view.getPixelValue(0, 0))

Pixels are referenced by x and y indices.

The results look like:

Image dimensions: [4, 3]

(0, 0) pixel value: ... band values ...

Source: https://code.earthengine.google.com/?accept_repo=users/gena/packages

Related Solutions

Google Earth Engine – Removing Specific Band from Image Composite

In order to remove particular bands from an image, you can take the image's bandNames, filter that list to only the bands you want, and select those bands from the image:

function removeMaxCorr(glcmImage) {
  return glcmImage.select(
    glcmImage.bandNames().filter(
      ee.Filter.stringEndsWith('item', '_maxcorr').not()));
}

Map.addLayer(removeMaxCorr(myImage.glcmTexture()));

(The pseudo-property name 'item' is the name used to refer to the value of a List item that isn't a feature with its own properties — here, a string.).

[GIS] Exporting ERA5 Image Collection data from Google Earth Engine

you will find documentation on this page : https://developers.google.com/earth-engine/python_install

I propose you to go through the native export tool of Earth Engine instead of geetools.

 import ee
 from google.colab import drive

Authenticate and mount your drive into your project

 ee.Authenticate()
 ee.Initialize() 
 drive.mount('/content/drive')

You can export images using a thread. I've never tried to export a whole collection but it seems to me that you can do it by replacing the 'image=image' attribute by 'collection=yourCollection' (not sure of that). In general, I prefer to transform my collection into an images list and then to upload images one by one.

imagesList = collection.toList(collection.size())
for i in range(0,imagesList.size().getInfo()):
  image= ee.Image(imagesList.get(i))
  #Process the export for you image into the folder of your choice into Drive 
  task = ee.batch.Export.image.toDrive(image= image,
    description='Exported from EarthEngine',
    fileNamePrefix='filename.tif',
    scale= scale,
    folder='repertoryOfYourChoice/',
    fileFormat='GeoTIFF')
 task.start()

Then you can follow the status of the last uploaded image in your list (you can upgrade this code by storing all the tasks in a list to track the status of all the images in your list) :

print(task.status())

Otherwise, about the scale it allows you to reproject an image to have a different resolution and speed up the export time. So it can be useful to use a large scale when working on very large areas. However, be careful not to scale it too large because the calculation time of the reprojection could sometimes be too greedy and exceed the maximum memory size allowed.

Best Answer

Related Solutions

Google Earth Engine – Removing Specific Band from Image Composite

[GIS] Exporting ERA5 Image Collection data from Google Earth Engine

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