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JeffLiedtke
Occasional Contributor II

The June 2017 update of ArcGIS Online includes some useful capabilities for displaying imagery served by your image services. These capabilities give you greater control for visualizing the information contained in your image services. When we talk about rendering, we’re not talking about making soap out of fat. Here at Esri, rendering is the process of displaying your data. How an image service is rendered depends on what type of data it contains and what you want to show.

Once you search for and add a layer, and your image is displayed in Map Viewer, click the More Options icon then Display to open the Image Display pane.

Image Display Options

You see a new category named Image Enhancement. This is where the real fun begins.

Image Enhancement pane

The Symbology Type options include Unique Values, Stretch and Classify. Unique Values and Classify renderers work with single-band image services, while the Stretch renderer works on both single and multiple band images.

Unique Values Renderer

Unique values symbolize each value in the raster layer individually and are supported on single band layers with Raster Attribute table. The symbology can be based on one of more attribute fields in the dataset. The colors are read from the Raster Attribute table and if they are not available the renderer assigns a color to each value in your dataset. This symbology type is often used with single band thematic data, such as land cover, because of its limited number of categories. It can also be used with continuous data if you choose a color ramp that is a gradient.

Unique Values Renderer

  1. Use the Field drop-down to select the field you want to map. The field is displayed in the table.
  2. Click the Color Ramp drop-down and click on a color scheme. If your image service already has a color ramp, such as the NLCD service in this example, it is displayed by default.
  3. The colors in the Symbol column and Labels can be edited as required.
  4. Click Apply to display the rendering in the layer

Stretch

The stretch parameters improve the appearance of your image by adjusting the image histogram controlling brightness and contrast enhancements. Either single or multiple band images can be stretched. For multiple band images, the stretch is applied to the band combination previously chosen in the RGB Composite options. The stretch options enhance various ground features in your imagery to optimize information content.

1.   Click the Stretch Type drop-down arrow and choose the stretch type to use. The following contrast enhancements determine the range of values that are displayed.

  • None – No additional image enhancement will be performed
  • Minimum and Maximum – Displays the entire range of values in your image. Additional changes can be made by editing the values in the Min-Max grid (available only when Dynamic range adjustment is turned off.)
  • Standard Deviation – Display values between a specified number of standard deviations
  • Percent Clip – Set a range of values to display. Use the two text boxes to edit the top and bottom percentages.

2.   If the Stretch type is set to an option other than None, the following additional image enhancement options will be available.

  • Dynamic range adjustment – Performs one of the selected stretches, but limits the range of values to what is currently in the display window. This option is always turned on if the imagery layer does not have global statistics.
  • Gamma – Stretches the middle values in an image but keeps the extreme high and low values constant.

3.   For single-band layers, you can optionally choose a new color scheme from the Color Ramp drop-down menu after applying a stretch method on the layer.

4.   Click Apply to display the rendering in the layer.

Here’s a WorldView-2 natural color image of Charlotte, NC, using the default no stretch:

Multispectral Image, No Stretch

And here is the same imagery layer with the top 2% and bottom 20% of the histogram omitted:

Multispectral Imagery, Percent Stretch

Classify Renderer

Classify symbology is supported by single band layers. It allows you to group pixels together in a specified number of classes. The following are the different settings available with the Classify symbology.

  • Field – Represents the values of the data.
  • Method – Refers to how the break points are calculated.
  • Defined Interval – You specify an interval to divide the range of pixel values and the number of classes will be automatically calculated.
  • Equal Interval – The range of pixel values are divided into equally sized classes where you specify the number of classes.
  • Natural Breaks – The class breaks are determined statistically by finding adjacent feature pairs between which there is a relatively large difference in data value.
  • Quantile – Each class contains equal number of pixels.
  • Classes – Sets the number of groups.
  • Color Ramp – Allows you to choose the color ramp for displaying the data.

Classify symbology works with single band layers that have either a Raster Attribute Table or Histogram values. If a histogram is absent, it is generated when you select the symbology type.

Here’s the classified map of Charlotte, specifying 15 classes and using the Natural Breaks method for determining class breaks:

Class Map

Summary

These new Map Viewer image rendering capabilities are similar to what you are used to in ArcMap and ArcGIS Pro. Since this release, Scene Viewer also supports imagery layers, however we are still working on bringing the new Map Viewer image rendering capabilities into Scene Viewer. Check out these new imagery capabilities in ArcGIS Online and see how they can enhance the stories behind your data.

Please leave us comments below for any future enhancements you’d like to see. And check back in a few months; we have a lot of other cool stuff planned for imagery in upcoming releases.

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ReneeBrandt
Occasional Contributor

image 1.PNGLandsat Polar image services.  Intrigued, I opened my email the other day, and was treated to some of the most gorgeous imagery of the Arctic and Antarctic I had ever seen.  Not only did the email contain the images you’ll see in this blog, but also links to two new applications I could use to explore the imagery in the regions and easily share it with others.

Let me give you an overview of the two new polar applications, Landsat Arctic and Landsat Antarctic, as I’m sure you are going to want to explore and share the information you find.

Esri’s Landsat Polar Applications

image2.pngFigure 3: Spectral profile view in Antarctic App

image 3.png

Figure 4: Time tool with cloud filter in Arctic App

Above, you can see screenshots of the Landsat Arctic and Antarctic applications, and some of the analysis tools built into the application. These applications support both visualization and analysis of the Arctic and Antarctic regions using polar stereographic projections required for working at these latitudes.   Using them, you can easily access the latest Landsat polar scenes without the need to store, compile, and process the source data onto your local machine. You have full access to the temporal multispectral, panchromatic, and pan-sharpened Landsat scenes. In addition, you’ll notice the variety of easy to use analysis tools we’ve included in the left hand side of the application.  These make it very easy to explore the imagery using custom band combinations, time profiles, and spectral profiles.

  • The Spectral profile functionality plots the spectrum of all bands for a desired selected pixel and
  • The Time profile provides a scalable timeline with the functionality to filter out clouds, simultaneously.

These applications also include new Facebook and Twitter links. Try them out. When you share the image you are looking at, the shared link will bring a user back to the same location and state of the image analysis that you were at. It’s a great capability for sharing the information and imagery that you find interesting with others. 

Landsat Polar Services

The Landsat polar services are available for use within the ArcGIS Online platform and are also part of the Living Atlas. These Landsat services and apps are open for public access. They can be directly used in ArcGIS Pro, ArcGIS for Desktop, ArcGIS Online web and mobile applications, as well as a wide range of applications that utilize the GeoREST Image Services API.

The services are sourced from the scenes that remain in their original UTM projections, but have been published as a services with a default polar projection. All reprojection and mosaicking is being performed on the fly. When viewing them in ArcGIS Online it is optimum to use the Arctic Polar Ocean Basemap / Antarctic Imagery Basemap. Other polar projections may be used within their useful limits.

These services can be used to support the work glaciologists and other scientists want to do in the polar regions including:  reducing uncertainties of ice sheet mass balance estimates, providing a streamlined way to investigate associated sea level rise, refinement of ice sheet models, measurement of ice surface displacement/motion, ice-sheet topography, tidal effects over floating ice, ice sheet surface albedo, estimate of surface melt rates, ice velocity, etc.

Accessing the various Polar services

image 4.PNGFigure 1: Arctic Service Figure 2: Antarctic service

(Full view with NDSI Colorized: Blue regions represent snow, water. Yellow-green regions are cloudy, rocky areas.)

The Arctic and Antarctic image services are separate and each is split into multispectral, panchromatic and pansharpened imagery. Currently the services contain all scenes collected since January 2015. In the Arctic, the GLS scenes that cover the Epochs of 2010, 2005, 2000, 1990, 1975 have also been added. The image services are updated daily to add new scenes as soon as they become available. Due to the fact that the Landsat satellite passes over the poles multiple times a day there is extensive temporal coverage. In the summer time when there is light and little cloud there is often a scene every day. Naturally in the winter months there is very little coverage.

Below is a visual representation of each of the 6 different Landsat Polar Services available, along with hyperlinks directing to them.

image 5.PNG             Landsat Arctic Views                     Landsat Arctic Pansharpened              Landsat Arctic Panchromatic   

    image 6.PNG       Landsat Antarctic Views               Landsat Antarctic Pansharpened         Landsat Antarctic Panchromatic

Similar to the Landsat World services, the polar services have various raster functions to render different band combinations and indices like Natural Color with DRA​, Geology with DRA, Color Infrared with DRA, Normalized Difference Moisture Index Colorized, and Panchromatic with DRA Sharpened. Two new raster functions Normalized Difference Snow index Colorized and Normalized Difference Snow Index Raw have also been introduced. Similar functions are available for the Antarctic service, as well.

For more information, see the Arctic Maps , Antarctic Maps or Landsat Community groups on ArcGIS Online. You can also access the Landsat World Web App from Unlock Earth’s Secrets.

Data Source

The imagery in these services is sourced from the U.S. Geological Survey (USGS) and the National Aeronautics and Space Administration (NASA). The data for these services reside on the Landsat Public Datasets hosted by Amazon on S3 storage.

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