Function for Visualizing AOP Image Collections in GEE

Writing a Function to Visualize AOP SDR Image Collections

In the previous Introduction to AOP Hyperspectral Data in GEE tutorial, we showed how to read in SDR data for images from 3 years. In this tutorial, we will show you a different, more simplified way of doing the same thing, using functions. This is called "refactoring". In any coding language, if you notice you are writing very similar lines of code repeatedly, it may be an opportunity to create a function. For example, in the previous tutorial, we repeated lines of code to pull in different years of data at SRER, the only difference being the year and the variable names for each year. As you become more proficient with GEE coding, it is good practice to start writing functions to make your scripts more readable and reproducible.

Let's get started! First let's take a look at the syntax for writing user-defined functions in GEE. If you are familiar with other programming languages, this should look somewhat familiar. The function requires input arguments args and returns an output.

var myFunction = function(args) {
  // do something with input args
  return output;
};

To call the function for a full image collection, you can use a map to iterate over items in a collection. This is shown in the script below.

// Map the function over the collection.
var newVariable = collection.map(myFunction);

For this example, we will provide the full script below, including the function addNISImage, with comments explaining what each part of the function does. Note that a helpful troubleshooting technique is to add in print statements if you are unsure what the code is returning. We have included some print statements in this function below, and show the outputs (which would show up in the console tab). Note that these print statements are commented out in the code linked with this tutorial, since they are not required for the function to run.

// Specify center location of SRER
var mySite = ee.Geometry.Point([-110.83549, 31.91068])

// Read in the SDR Image Collection
var NISimages = ee.ImageCollection('projects/neon/DP3-30006-001_SDR').filterBounds(mySite)

// Create a function to display each NIS Image in the NEON AOP Image Collection
function addNISImage(image) { 
// get the system:id and convert to string
  var imageId = ee.Image(image.id);
  // get the system:id - this is an object on the server
  var sysID_serverObj = ee.String(imageId.get("system:id"));
  // getInfo() converts to string on the server
  var sysID_serverStr = sysID_serverObj.getInfo()
  print("systemID: "+sysID_serverStr)
  // truncate the string to show only the fileName (NEON domain + site code + product code + year)
  var fileName = sysID_serverStr.slice(46,100); 
  print("fileName: "+fileName)
  // mask out no-data values and set visualization parameters to show RGB composite
  var imageRGB = imageId.updateMask(imageId.gte(0.0000)).select(['band053', 'band035', 'band019']);
  // add this layer to the map
  Map.addLayer(imageRGB, {min:2, max:20}, fileName)
}

// call the addNISimages function
NISimages.evaluate(function(NISimages) {
  NISimages.features.map(addNISImage);
})

// Center the map on SRER
Map.setCenter(-110.83549, 31.91068, 11);

Note that the first half of this function is just pulling out relevant information about the site - in order to properly label the layer on the Map display. You should recognize some of the same syntax from the previous tutorial in the last two lines of code in the function, defining the variable imageRGB, using updateMask, and finally using Map.addLayer to add the layer to the Map window. Note that this function is subsetting the SDR image to only pull in the red, green, and blue bands, as opposed to the previous tutorial where we read in the full hyperspectral cube, and then displayed only the RGB composite in the visParam variable.

You can see that the print statements are showing up in the console, displaying the systemID and fileName for each image in the collection. The fileName is applied to the name of the layers in the Map window.

You could alter this function to include the visualization paramters, to subset by other bands, or modify it to work for a different image collection. We encourage you to do this on your own!

Get Lesson Code

Function to display AOP SDR Image Collections in GEE