How to download ASTER GDEM in various ways?

In this post, I will show you how to download Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) Global Digital Elevation Model (GDEM) version2 in different ways from the http://gdem.ersdac.jspacesystems.or.jp/index.jsp website at no charge.

But at first, a quick introduction to ASTER GDEM

The ASTER GDEM was developed jointly by the Ministry of Economy, Trade, and Industry (METI) of Japan and the United States National Aeronautics and Space Administration (NASA). This highly accurate global dem covers land surfaces between 83°N and 83°S and is comprised of 22,600 (1°-by-1° or 3601-by-3601 pixels) tiles. Tiles that contain at least 0.01% land area are included. It is available in GeoTIFF signed 16 bits output format with geographic lat/long coordinates and a 1 arc second (approximately 30 m) grid. It is referenced to the WGS84/EGM96 geoid. 

By utilizing the ASTER GDEM as a base data, users can perform many types of spatial analysis such as: 

• Surface/Terrain analysis involves extraction of new information such as slope, aspect, Hillshade/shaded relief, contour etc. from the dem 
• The hydrological analysis allows you to identify sinks, determine flow direction, calculate the flow accumulation, delineate watersheds, and create stream networks from the dem 
• Viewing and navigate space within a 3D planimetric view
• Line-of-sight analysis 
• Flight simulation And many more….. 

How to Download?

As I mentioned above, go to the http://gdem.ersdac.jspacesystems.or.jp/index.jsp  link and at first register yourself. So click the Register & Modification option  present on the left side of the index page.

Now, input user information either as an Organization or a Personal (below figure).

Click Next Button and Entry Confirmation window come (below figure).

Finally, click Register button, so again you come to the main page ( but this time you are logged in with your specified user name (below figure).

 

After successfully registering yourself, click Search button to find out the required area of interest for downloading dem tiles.

Once you come in the search page, choose any one of the following four tile selection options:
(1)  Select tiles directly  (2) Select tiles by polygon  (3) Select tiles by shapefile  (4) Select tiles by coordinates.
Although you can choose any one of the above four options for dem tiles selection purpose, I explain all the four options one by one.

Select tiles directly   

Choose Select tiles directly tab. Click #Grid button to show 1 degree x 1 degree tiles grid in the map. Then click Start button. Zoom the map by dragging the slider bar towards right.

Now, move the cursor along the center of the grid approximately, it shows the latitude and longitude values of the cursor locations at the bottom. Select following three grids that cover the Darjeeling district of West Bengal, India.

Click Next button from the bottom of the window, it shows the tile list(see below figure).

Again click Next button, and download all these three zip files along with readme file in proper location.
Select tiles by polygon 
Choose Select tiles directly tab. Click Start button and draw a polygon to select three grids that cover the Darjeeling district of West Bengal, India (see below figure). Click OK button twice to fix the polygon. Click Next button from the bottom of the window, it shows the tile list as mentioned in the above section and the same way download these three zip files.

Select tiles by shapefile
Here, we select tiles by an existing shapefile ‘darjeeling_outline.shp” that you found here download Darjeeling.rar file .
Extract this rar file and store the darjeeling_outline.shp file in a proper folder. In our case it is in dem folder. Now specify this shape file using Browse button as per below figure.

Then click OK button, it selects three tiles as per the spatial extent of the darjeeling_outline.shape file (see below figure).

Now click Next button from the bottom of the window, it shows the tile list as mentioned earlier. Now download each and every individual zip file (see below figure).

Select tiles by coordinates
Choose Select tiles directly tab. Specify following latitude-longitude ranges:

And click Ok button. Then in the Fix region message window, click OK button (see below figure). 

Notice that four tiles are selected, although we need only three of them. Click Next button. Uncheck following tile that is outside of our area of interest and download remaining three tiles.

So, whatever the above mentioned methods you follow to download ASTER GDEM tiles, ultimately, get the three zip files such as (1) ASTGTM2_N26E088.zip (2) ASTGTM2_N27E087.zip and (3) ASTGTM2_N27E088.zip.

Extract these three zip files in a suitable location, and get corresponding three folders (see below figure) that contain the three dem images.

Now, copy ASTGTM2_N26E088_dem.tif, ASTGTM2_N27E087_dem.tif and ASTGTM2_N27E088_dem.tif from the above mentioned three folders and store in a new folder in our case it is in ASTER_DEM folder.

That’s all, very soon in the next post  I will discuss how to perform basic image processing and hydrological analysis using these downloaded ASTER DEM data.

Use QuantumGIS that can compete with any other popular GIS Software

For those of you still hesitate to use open source desktop GIS software “Quantum GIS or QGIS”, here are some strong reasons to use it now.

1. QGIS is free and open-source software (FOSS)

Anybody with an Internet connection can visit http://www.qgis.org/en/site/ site and retrieve a copy of the GIS software.  There is no cost to the user and this software’s source code is also freely available for the users to make any changes to the program.

QGIS can also run on many operating systems, including Windows, Mac OS, Linux, and UNIX. It has a small file size compared to commercial GIS's and requires less RAM and processing power; hence it can be used on older hardware or running simultaneously with other applications where CPU power may be limited.

2. View data

You can view and overlay vector and raster data in different formats and projections without importing/exporting. Supported formats include:

• QGIS uses the OGR library to read and write vector data formats, including shapefiles, MapInfo TAB file formats, GML, KML, AutoCAD DXF, PostGIS, SpatiaLite, Oracle Spatial and MSSQL Spatial databases, and many more.
• Raster formats supported by the installed GDAL (Geospatial Data Abstraction Library) library, such as GeoTIFF, ERDAS IMG, ArcInfo ASCII GRID, JPEG, PNG and many more.
• Online spatial data served as OGC Web Services, including WMS, WFS and many more.

3. Extend QGIS functionality through plugins

QGIS can be adapted to your special needs with the use of extensible plugin programs that can greatly enhance the functionalities of the software. 

4. Print Composer

With the Print Composer you can create nice maps and atlases that can be printed or saved as PDF-file, an image or an SVG-file. This is a powerful way to share geographical information produced with QGIS that can be included in reports or published. 

5. Working with GPS Data 

The GPS receiver uses the signals from the satellites to calculate its latitude, longitude and (sometimes) elevation. Most receivers also have the capability to store locations (known as waypoints), sequences of locations that make up a planned route and a tracklog or track of the receiver’s movement over time. Waypoints, routes and tracks are the three basic feature types in GPS data. QGIS displays waypoints in point layers, while routes and tracks are displayed in linestring layers. 

QGIS can also perform Live GPS tracking so If the GPS receiver is receiving signals from satellites, you will see your position in latitude, longitude and altitude together with additional attributes on the QGIS map. 

6. Create, edit, manage, analysis and export data 

• Ability to create and edit shapefiles 
• Image georeferencing
• Support for visualizing and editing OpenStreetMap data
• Improved handling of spatial database tables 
• Tools for managing vector attribute tables 
• Option to save screenshots as georeferenced images
• Offers vector analysis, spatial query, shortest path analysis,sampling, geoprocessing, geometry, database management tools and many more
• Offers many raster analysis, such as terrain analysis, zonal statistics, conversions, dam creation etc. 

7. Basemap Facility 

You can easily add a number of popular image services as base maps to publish your own GIS map. Name of the such image services are Google map, OpenStreetMap, and Bing maps.