Visual Terrain Elevation Database of China
Horizontal 90m resolution DEM

InforShell CN3SDEM Professional Edition Introduction


  • Overview

  • Coverage and Resolution

  • Data Source

  • Scaling Relationship Between Layers

  • DEM Visualization Details

  • Using DEM to Aid Aerial Navigation
  • 3D Visualization of DEM

  • Searching for Target Elevations

  • Adding Custom Data

  • System Requirements & User Directions

  • Contact Us

  • Download Software Demo

  • Overview

    Visual Terrain Elevation Database of China (CN3SDEM) is created from 90m resolution DEM data. InforShell constructed the CN3SDEM by mosaicing together thousands of data files and images, and importing China's regional boundaries, provincial, city and longitude/latitude information.

    CN3SDEM includes a richly-featured eEarth browser that allows you to:

  • View a seamless true or false color shaded relief of the DEM, and read numerical elevation data and coordinates of the image pixel under your mouse cursor.
  • Jump to location by searching for province or city name or longitude-latitude coordinates.
  • Simulate different sun positions and terrain coloring to improve accuracy of shaded relief for aerial navigation.
  • View and control a 3D visualization of the DEM.
  • Using CN3SDEM as background, plug-in custom data, connect to GPS, calculate distance between two points, and area between many points etc.
  • The database and browser are portable, so it can be run effectively on a laptop for field work.

    Figure 1. CN3SDEM true color shaded relief

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    Coverage and Resolution

  • Continuous coverage of mainland China, main islands (including Taiwan, Hainan Island), and other areas within the national boundary of China.
  • Each pixel spans 3 seconds in longitude and 3 seconds in latitude, i.e. horizontal resolution of 90m.

  • eEarth resolves elevation data to 1m precision.

  • The DEM does not include valid data for water, snow and ice covered areas.
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    Data Source

  • The Digital Elevation Model (DEM) used in CN3SDEM is distributed by NASA at 90m horizontal resolution.

  • The true color satellite imagery is distributed by NASA at 1km resolution .

  • The national and provincial boundaries, as well as provincial and city names of PR China are distributed by China Ministry of Geology

  • The 2.5D shaded relief and false color visualizations are generated by InforShell.

  • Scaling Relationship Between Layers

    Layer 0: Horizontal resolution of 30 arc seconds (1km)

  • A true color surface to the DEM, composed of satellite imagery.

  • Overlaid national and provincial boundaries of China.

  • Projection to Layer 1 at 1:10 in each dimension.
  • Layer 1: Horizontal resolution of 3 arc seconds (90m)

  • A composite layer consisting of 2.5D false color shaded relief and numerical DEM data;

  • Imported provincial and city names of China.

  • Note: Due to limited resolution of the official provincial and national boundaries vector diagram, it is not suitable for display at the 90m resolution, and hence not overlaid on Layer 1.

    Use of Original DEM Data

  • The original DEM (numerical value) can be read when your mouse cursor is hovering over Layer 1 imagery.

  • Custom false color shaded relief and 3D visualizations are computed and painted inside eEarth using the original DEM data dynamically as you operate.

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    Figure 2. True color satellite image and Chinese provincial boundaries (layer 0).

    DEM Visualization Details

    InforShell used a proprietary high resolution data visualization engine to process the DEM and generate the 2.5D true or false color shaded relief imagery.

    1. Elevation based color scheme:

  • A color gradient from green to red was used to represent DEM data ranges from 1m to 9000m.

  • Invalid data in mountainous regions and bodies of water were colored blue.
  • 2. Elevation based relief shading:

  • The DEM was processed at 1m vertical resolution.

  • Default sun position was assumed to be northwest.

  • On illuminated sides, increasing brightness gradient was applied according to elevation rise (and similarly, decreasing brightness gradient applied according to elevation drop on shadowed sides.)
  • 3. Continuity across multiple DEM source files:

  • The original DEM, in one by one degree files, were processed to generate the shaded relief images.

  • A total of 1121 images, covering all of China, was mosaiced together and stored in database.

  • Note: Images are in compressed format when stored in database.

    4. Mapping DEM data to shaded relief:

  • The 1121 DEM files were mosaiced together and imported into database.

  • Each pixel of shaded relief projects to one DEM data point..
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    Figure 3. Shaded relief with sun position set to northwest.

    5. 2.5D shaded relief image provides indexing to DEM numerical data:

  • The elevation values can be read when your mouse cursor is hovering over shaded relief imagery.

  • Shaded relief helps you quickly identify terrain features (e.g. mountainous areas, hills, rivers, and plains).

  • Using DEM to Aid Aerial Navigation

    When natural disasters occur in mountainous regions, requiring emergency aerial rescue, terrain appearance seen from above will differ during different times of day.

    eEarth has built in shaded relief algorithm that can repaint the shadow direction based on user specified sun position. This will help make the generated image resemble actual scenes and facilitate aerial navigation use.

    1. Sun position adjustment:

  • Supported sunlight direction are: east, south east, south, south west, west, northwest, north and north east.

  • On illuminated sides, an increasing brightness gradient is applied according to elevation rise (and similarly, a decreasing brightness gradient is applied according to elevation drop on shadowed sides.).
  • 2. Vegetation color adjustment:

  • You can select from a color palette to repaint the terrain to resemble desert, plateau, or desired chlorophyll colors.
  • Note: Sun position adjustment and vegetation color adjustment can be applied at the same time.

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    Figure 4. Sun position set to northwest.

    Figure 5. Sun position set to southeast, same location as shown in Figure 4.

    3D Visualization of DEM

    Mouse driven active area:

  • You can view a 3D visualization of any area of the DEM by clicking on the shaded relief image - this starts immediately a 3D visualization window.

  • You can adjust the 3D rendering for a desired perspective by dragging it with your mouse cursor.

  • While the 3D visualization window is open, you can visualize different areas by driving your cursor (right click and hold) on the shaded relief image.
  • 3D visualization options:

  • True color or false color surface.

  • Wireframe view.

  • Adjust brightness.

  • Control surface color smoothing.

  • Control elevation data smoothing (low pass filter).
  • Effects of smoothing:

  • You have the option of choosing from 0 - 11 for smoothing level.

  • For example, at 4km resolution level 7 gives smooth 3D visual results; at 1km resolution level 5 gives smooth 3D results, and at 90m resolution, no smoothing is necessary to portray smooth terrain.
  • Figure 6. 3D visualization of DEM (90m layer) using true color shaded relief surface.

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    Figure 7. 3D visualization of DEM (90m layer) using false color surface.

    Figure 8. 3D visualization of DEM (90m layer) using false color surface with grid.

    Searching for Target Elevations

    Data analysis features:
    Through eEarth, you can search for an elevation of interest by applying these comparison operators: below, above, equal, not equal, or between. Areas matching these criteria can be highlighted, or areas not matching the criteria can be pained gray. Highlighted areas can further be shown transparent or opaque.

    Usage example:

  • If certain plant species are of interest, areas matching their favored elevations can be easily identified.

  • Areas in danger of flooding can be determined based on estimations for dam failure thresholds.
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    Figure 9. Filtered image using specific elevation criteria.

    Adding Custom Data

    User Notes
  • You can add location based notes and tracks on the shaded relief using the "Set user note" and "Set user track" features. Each note will be shown as a clickable symbol on the image background.

  • Symbols and routes added by the user can be saved to file. These small files can be easily shared (over email for example) between multiple parties.
  • Static Data

  • Static data includes positions of buildings or facilities such as railways, roads, power networks, gas pipelines etc.

  • Static data in vector diagram format can be directly imported into database using InforShell's GADB software.

  • Vector diagram using the MapInfo data format can also be imported into database using GADB.
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    System Requirements & User Directions

    CN3SDEM has excellent portability in the standard Windows PC environment.

    Accessing CN3SDEM:

  • No installation is required.

  • Copy all contents of the CN3SDEM DVD-ROM onto your hard drive. Double click the browser program "eEarth.exe" to start.

  • eEarth does not require user training, its design is consistent with the style of MS Windows.

  • Multi-user sharing of CN3SDEM in a LAN environment is supported.
  • System Requirements:

  • MS Windows Chinese Edition NT2000, XP or Vista

  • MS Windows ODBC and MS Access Driver.
  • Contact Us

    For questions about CN3SDEM professional edition, or to obtain a quote, please contact us at

    If you're interested in finding out more about this product, please try our full-featured software demo (the geographic coverage is reduced) available for download here (Zip file 91MB).

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