USGS Global Visualization Viewer: Help

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USGS Global Visualization Viewer: Site Description

The USGS Global Visualization Viewer (GloVis) is a quick and easy online search and order tool for selected satellite data. The viewer allows user-friendly access to all available browse images from the Landsat 7 ETM+, Landsat 4/5 TM, Landsat 1-5 MSS, EO-1 ALI, EO-1 Hyperion, MRLC, and Landsat Orthorectified data sets, as well as Aster TIR, Aster VNIR and MODIS browse images from the DAAC inventory. Through a graphic map display, the user can select any area of interest and immediately view all available browse images within the USGS inventory for the specified location. From the browse image viewer page, the user may either navigate to view adjacent scene locations or select a new area of interest. GloVis also offers additional features such as cloud cover limits, date limits, user-specified map layer displays, scene list maintenance, and access to metadata. An ordering interface is available for Landsat, EO-1, MRLC, Landsat Orthorectified, ASTER and MODIS data purchases. Future GloVis releases will include the addition of data from other sensors within the USGS EROS archives.

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USGS Global Visualization Viewer: Home Page

Latitude and Longitude

The Latitude and Longitude form elements serve a dual purpose. Entering a latitude and longitude using the keyboard and clicking the View Images button will activate the Browse Image viewer window, which will display a mosaic of browse images centered on the selected location. The Latitude and Longitude form elements also display the latitude and longitude as the mouse cursor moves over the Locator Map.

Sensor

The USGS Global Visualization Viewer defaults to searching the Landsat 7 ETM+ archive. The other available sensors may be selected from within two dropdown lists.

View Images

Clicking the View Images button activates the Browse Image viewer window centered on the latitude and longitude entered in the Latitude and Longitude form elements. If no latitude and longitude values are entered, the Browse Image viewer window will center on a default location.

Locator Map

The global locator map of the world is displayed in the geographic projection, and includes limited cultural boundaries and shorelines. Clicking on any location within the locator map activates the Browse Image viewer window centered on the latitude and longitude selected.

What's New!

Describes all modifications and improvements included within the current release of the USGS Global Visualization Viewer.

Quick Start Guide

Provides a brief overview on using the USGS Global Visualization Viewer.

Browser Requirements

Provides a list of suggested browser and software requirements, and describes any known problems associated with particular browsers and/or operating systems.

Help (This page)

Provides general user information on controls, navigation, and functionality of the USGS Global Visualization Viewer.

About Browse Images

Provides information and Frequently Asked Questions (FAQs) regarding the USGS Global Visualization browse displays.

Download Source Code

Provides a link to a web site that allows downloading the source code used to produce the USGS Global Visualization Viewer web site. This code will only be of interest to people interested in creating similar web sites.

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USGS Global Visualization Viewer: Browse Image Viewer

The Browse Image Viewer page opens the Browse Image Viewer application in a separate window. Note that the web browser has to remain on the page to keep the application displayed.

The Browse Image Viewer application is implemented as a Java applet. It works with either the web browser's built in version of Java, or with the Java plug-in available from Sun. Note that some of the features are only available when using the Java plug-in from Sun (or a browser with an equivalent built-in version of Java). These features also require the user to answer "yes" to the security warning dialog that is displayed before the Browse Image Viewer application is shown. Answering "yes" to the security warning dialog grants the application the privileges required to access the user's local hard drive. The application uses this to do things like save the contents of the scene lists to the user's computer and reload them later at the user's request. Answering "Always" is the same as answering "yes", and will eliminate needing to answer the question on future visits to the web site.

The viewer application has four basic components: the menu bar, the controls on the left side of the main window, the browse images displayed on the right side, and the status bar.

The Browse Image Viewer application uses separate threads of execution for downloading data from the GloVis server. While data is being read from the server, various indicators are displayed in the image area of the display. The indicators describe what is being read, such as "Reading Inventory" to indicate the list of available scenes is being read, "Loading Imagery" to indicate browse images are being read, or "Loading Map Layers" to indicate map layers are being loaded. While images are loading, a coverage map is drawn in light blue to indicate where scenes are being loaded. The user can still interact with the applet while data is being read from the server, although some functions may be disabled temporarily.

Note: The viewer application window typically displays a line with a message "Java Applet Window". The location of this message varies depending on the Java implementation and Operating System being used.

Menu Bar

The Browse Image Viewer has a menu bar at the top of the application window to provide an interface to many of the options available in the viewer. The following paragraphs provide details on each of the available menu entries.

NOTE: On an Apple Macintosh, the menu bar selections are added to the menu at the top of the display instead of directly to the application window.

Navigation Controls

The left side of the application window has various naviation controls that are explained in the following paragraphs.

Image Display Area

The right side of the application window displays browse images and map layers for the currently selected sensor and viewing area. The following paragraphs provide some details on the image display area.

Status Bar

The bottom of the Browse Image Viewer application window displays a status bar for the application. The status bar is separated into three areas. Those three areas provide the following information (from left to right):

Tools Menu Options

The Browse Image Viewer provides several tools under the Tools Menu that allow interacting with the application. Most of the options open a dialog box. The options are described in the following paragraphs.

File Menu Options

The Browse Image Viewer provides several tools on the File Menu for interacting with the application. The details of these options are described in the following paragraphs. Note that these options are only available when using the Java plug-in and the GloVis applet was granted sufficient privileges by the user answering "yes" to the security warning dialog that is displayed before the applet loads. If both of these conditions are not fulfilled, the File menu will not be available.

Forum

The GloVis forum provides users the opportunity to ask questions, discuss topics, share information and obtain answers regarding the GloVis website, the data products offered and remote sensing tips. Users do not need to register to review the forum; however, registration is necessary to interact within the forum.

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Frequently Asked Questions (FAQs)

Q: Where is the geographic location displayed?

A: As your cursor is passed over the locator map or any browse image, the geographic location is reported in the browser status bar (lower left margin of your browser window). The latitude and longitude is displayed in decimal degrees. For the locator map, the path and row (or tile number) under the cursor is also listed.

Q: Why such long response times?

A: Loading nine Landsat graphic images of 30-40K each, or dozens of ASTER graphic images of 5K each, may take from a few seconds up to 1.5 minutes, depending upon your internet connection. Once a set of browses has been cached, the response time should improve. Recently, the browse image viewer was improved to allow the user to continue interacting with the viewer while images are being downloaded.

Q: Why do some images appear to be tilted sideways?

A: This is an artifact of the Lambert Azimuthal Equal Area projection, which will produce more skewing near the edges of a region. Just remember that for any scene, North is pointing from one row to the row above it, and not necessarily towards the top of your page.

Q: Why do the scenes sometimes look misaligned in the mosaic view?

A: The browse scenes used to create the Global Visualization inventory only have approximate geographic information available. This sometimes leads to inaccurate placement of the scenes.

Q: Why do some scenes appear to be "missing"?

A: There are several possible reasons:
  • Landsat:
    1. The satellite does not acquire some areas of the world. For example, the Landsat program does not typically acquire data over oceans.
    2. The viewer will only display scenes that exist in the USGS archive. For many locations outside the U.S., there may be scenes that were collected by the sensor but the data is not archived or distributed by USGS EROS. These scenes may still be available from other International Ground Stations. (Please note that this data is not a product of USGS EROS; therefore, the price, available formats, and/or processing options may vary according to the data provider.)
    3. The viewer will only display scenes that have browse images available in the USGS inventory. Some scenes (particularly Landsat 5) do exist in the USGS archive, but they do not yet have a corresponding browse image. To access Landsat 5 TM data for which there is no browse, you will need to run a search on Earth Explorer. As the TM browse images become available in the future, they will be continually added to the USGS Global Visualization tool.
    4. Different regions of the world are displayed using different parameters for the Lambert Azimuthal Equal Area projection. In the areas where two of these regions meet, only data from one of the regions can be displayed at a time. This will be corrected at some point in the future.
  • ASTER and EO-1:
    1. ASTER and EO-1 scenes are typically collected on-demand. The programs do not attempt to get full coverage like the Landsat program.
    2. Different regions of the world are displayed using different parameters for the Lambert Azimuthal Equal Area projection. In the areas where two of these regions meet, only data from one of the regions can be displayed at a time. This will be corrected at some point in the future.

Q: Why doesn't the URL update when navigating, and why can't I save a bookmark that shows the viewer window that was last displayed when the bookmark was created?

A: The image browser web page is an independent Java applet, so any actions within the applet (such as selecting a new location, selecting a new date, and changing the viewing mode) will not ever affect the main URL to which the browser is pointed.

Q: Why does the "BACK" button take me all the way back to the home page, rather than to the browse image I was viewing last?

A: The image browser webpage is an independent Java applet, which means the URL is not changing as a search is run. Selecting the "Back" button of the browser window will only take you to the previous screen (URL), which is the home page.

Q: How can I print or save a browse image?

A: If you want to print a single browse image, the best way is probably to use the "Show Browse" feature to open a separate window which will allow the user to print and/or save the browse image. Metadata can be printed in the same way using the "Show Metadata" feature. The original browse images and metadata can be downloaded using the options in the File menu. There is also a print option under the Tools menu that will print the entire main window of the Java applet.

Q: What if I want to purchase precision- or terrain-corrected Landsat data?

A: The Landsat Orthorectified products and MRLC 1992 and 2001 datasets that are available through the Global Visualization Viewer (GloVis) are terrain corrected. However, other Landsat data products need prior approval to purchase precision- or terrain-corrected data. GloVis now utilizes a new feature through the Earth Explorer Shopping Basket that allows users to login from different applications. If you are approved to purchase precision- and terrain-corrected data, those options will be available in the Shopping Basket after you login. Note: Under current USGS policy, the distribution of precision- and terrain-corrected data is restricted to only USGS researchers for Landsat 7 ETM+, and to only Approved U.S. Government and its Affiliated Users (USGAU) for Landsat 4/5 TM and Landsat 1-5 MSS.

Q: Why do latitude and longitude grid lines sometimes appear in the water map layer?

A: The source used by GloVis for the water map layer contains the latitude and longitude grid lines. In the future, we may be able to locate a data source that does not contain the grid lines.

Q: Why are the Latitude, Longitude, and Select Sensor selection boxes on the Home page not displaying or fully displayed on the page?

A: The browser is configured to use a larger font than the page is designed for. To change your browser font configurations do the following according to the type of browser you are using.
  • Netscape 6.0+
    1. From the menu bar on your browser window, click on View.
    2. Then click on Text Zoom and select any size of text that is 100% or lower.
  • Internet Explorer 5.0+
    1. From the menu bar on your browser window, click on View.
    2. Then click on Text Size and select either medium, smaller, or smallest.

Q: Why do I occasionally receive an empty page (site) when I try to submit an ASTER, Orthorectified, or MODIS data order?

A: Orders for these datasets are placed through the EOS Data Gateway (EDG). If the EDG is experiencing downtime, orders cannot be placed. The EDG has a scheduled downtime every Wednesday morning, so it is best to wait until the afternoon on Wednesdays to place orders. The EDG sometimes experieces unscheduled downtimes during the week. To help out in both of these situations, restore options have been implemented in the SceneList and Scene List Dialog Box that will repopulate the scene IDs as they were listed before the order button was used.

Q: Why does the Shopping Basket, Metadata, or Browse Image fail to appear when I click the 'Order', 'Show Metadata', or 'Show Browse' buttons?

A: This is usually caused by a browser or 'add-on' security product that incorrectly blocks pop-up windows that it should not be blocking. In GloVis, the shopping basket, metadata, browse image, and other windows can be affected by this. Refer to your browser or add-on security product documentation to learn how to disable the pop-up blocking for the GloVis web site. The following products have been known to cause problems:
  • Windows XP Service Pack 2 added pop-up window blocking to Internet Explorer.
  • The "Google search bar" that can be added to browsers has an option to prevent pop-up windows from appearing.
  • Some 'add-on' security products (like Norton Internet Security and others) have a feature to block pop-up windows.
Note: Some of the products allow temporarily bypassing the pop-up blocker by holding down the "Control" key when clicking on a button that pops up a window.

Q: Why do the dates for some of the MODIS images on GloVis not correspond with imagery for the same date provided through the MODIS Rapid Response System?

A: The data from the Rapid Response System (rapidfire) site are daily data collections. The MODIS products on GloVis are a collection of both daily and composite products.Refer to the About Browse page for a description of which datasets are daily and which are composites. As the daily data and multi-day composites are different products, they won't look the same and the dates won't be the same. The date that appears in the Scene Information field for daily data is the acquisition date, but for multi-day composites it is the first date of the collection period.

Q: Why do I get a page indicating I need a newer version of Java?

A: GloVis requires Java 1.4 or newer. If the version of Java detected is older than that, the page indicating a new version of Java needs to be installed is displayed. The page provides instructions for updating Java. Note that some browsers do not allow the version of Java to be detected properly and this page might be displayed when the required Java support is already installed. A link to go to the GloVis applet page is provided, but the page will not work if Java 1.4+ is not installed.

Q: If I update to a newer version of Java, will it erase my existing version of Java?

A: No. It installs a newer version of Java while leaving the existing versions intact. This is useful for a site that has only certified their application on an earlier version, and another site that requires a newer version.

Q: How do I download Imagery?

A: When the "free scene download" message is shown in the image display area, the full resolution data may be downloaded for free. To download the imagery, first select (click on) the scene you would like to download. Then on the bottom portion of the left panel under 'Scene List', click 'Add' and the scene will be added to the list. The scene will be highlighted in the 'Scene List' box, and the 'Download' button will become available. For each scene, click the 'Download' button. A pop-up box will appear informing you of the amount of time the download will take and asking if you would like to continue. To download, click 'Yes'.

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Contact Customer Services

Customer Services
U.S. Geological Survey
Earth Resources Observation & Science (EROS)
47914 252nd Street
Sioux Falls, SD 57198-0001

Tel: 800-252-4547
Tel: 605-594-6151
TDD: 605-594-6933
Fax: 605-594-6589
Email: custserv@usgs.gov
Business Hours: Monday thru Friday, 8:00 a.m. to 4:00 p.m., central time

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