The Elevation Library Manager provides a method to collect and manage your elevation source files, including Digital Elevation Model data (DEM), as well as Digital Terrain Elevation Data (DTED) used by the U.S. National Geospatial-Intelligence Agency.
For more information on these data types, see Topographic Data in the Producer Field Guide.
See below for details on the following:
- Global Elevation Source File
- Creating an Elevation Library
- Adding Elevation Source Files to Elevation Library Manager
- Scan Data
- Session Log Report
- Elevation Values Reported in View Status Bar
- File Requirements for Use in Elevation Library Manager
- Dialog Description
- Using the Elevation Library
- Preference to Automatically Use Elevation Library
Many companies and agencies maintain data holdings of elevation data used for ortho-rectifying data and other terrain-related purposes. The elevation data is generally of multiple resolutions covering different spatial locations - perhaps a global elevation dataset which covers everywhere the company might be interested in at a lower resolution and then a patchwork of higher resolution data sets and tiles covering locations which have been studied in more depth.
How do you select (or even find) the best elevations source data for the locations you are interested in and how do you patch together potentially multiple tiles (at potentially multiple resolutions)? For example - you want to improve the spatial accuracy of coordinates read from GeoEye IKONOS imagery by associating it with a DEM (rather than using the constant elevation normally referenced by the header). How do you pick the correct elevation files to use?
ERDAS IMAGINE provides a potential solution to this issue - the Elevation Library Manager. The Elevation Library Manager provides a method to collect and manage your elevation source files, including Digital Elevation Model data (DEM), as well as Digital Terrain Elevation Data (DTED) used by the U.S. National Geospatial-Intelligence Agency.
The Elevation Library Manager simplifies elevation source file organization by storing the locations and relevant files of elevation data in a prioritized list. You can store multiple directories containing multiple elevation source files in the list, and store individual elevation source files.
Multiple Elevation Source Files
Global Elevation Source File
The Global Elevation Source file, provided by ERDAS, is listed in the Elevation Library Manager as an Elevation Source. The file is located in <IMAGINE_HOME>/etc directory. Named GlobalElevationSourceProxy.esl, it contains parameters and the path to the global DEM, a virtual mosaic of elevation data for the entire Earth. The global DEM, located in <IMAGINE_HOME>/etc/globalterrainsources directory, is named globaldem2.jp2.
Creating an Elevation Library
Adding Elevation Source Files to Elevation Library Manager
- In the Ribbon, open the Elevation Library Manager dialog by clicking Terrain tab > Elevation Library.
- Click [Add File] to add individual DEMs or DTEDs to the CellArray list to be scanned.
You can also click [Add Directory] to add a directory structure to the list to be scanned.
- Sort them according to the priority in which you want them to be used according to their position in the CellArray, where Row 1 is used first and the next rows are used consecutively. The highest resolution files will have higher priority.
See Add, Sort, and Remove Data, below, to add, sort, and remove data from the Elevation Library Manager.
- Click OK to scan the directories and files to test if they meet the File Requirements for Use in Elevation Library Manager, below, to be used in the Library.
- Open the Session Log to review the messages to see which files were added, or not added, depending on which option is selected in Logging level. See Example of Session Log Report, below.
- Return to the Elevation Library Manager dialog, and remove any files that do not meet file requirements.
Elevation Values Reported in View Status Bar
- Once your Elevation Library is set up, in order for elevation information to be reported in the View Status Bar, go to the Elevation Library preference and click to check (turn on) the Sensor models should auto-associate option.
- When the image is displayed, the data is resampled on-the-fly to the finest pixel size of the files in the Elevation Library using bilinear interpolation method.
File Requirements for Use in Elevation Library Manager
- Supports only raster type DEMs and DTEDs.
- Imagery must have an associated 3D (projective) sensor model either via calibration or embeddded in a NITF or TFRD image.
- The elevation source file will show as a raster file type if it is visible in the File Selector as a File of type All File-based Raster Formats.
- The elevation source file must have projection information and be using the Geographic (Latitude/Longitude) map projection.
- The elevation source file must have elevation information.
- All of the files in the library must have the same vertical datum and units.
- The coordinate system of all of the files in the library must match.
This dialog opens when you select Terrain tab > Elevation Library.
Elevation Sources This area of the CellArray displays a list of elevation source files and directories that will be checked to see if they meet the file requirements (see above) tests to be included in the Library.
The order of directories and files in the CellArray determines the order in which the elevation sources are used. The directory or file listed in Row 1 is used first as the source of elevation data.
Add, Sort, and Remove Data
[Add directory] Click to add a directory to the Elevation Sources list. The File Selector dialog opens. You can select an existing directory or create a new directory.
[Add file] Click to add a file to the Elevation Sources list. The File Selector dialog opens.
[Remove item] Click to remove the selected Elevation Source file from the Elevation Library. This does not delete the file from disk; rather it just removes the file from the configured Elevation Library.
[Move up] Click to move up the selected directory or file in the list making it a higher priority.
[Move down] Click to move down the selected directory or file in the list making it a lower priority.
Logging level: This filters the messages that you receive in the Session Log when you click OK to test to see if your elevation source files meet the file requirements (see above) for use in Elevation Library Manager. Select one of the options below as a filter.
Open the Session Log to see the reported errors and messages.
Errors only This option has the Session Log report any actual errors encountered while looking for valid DEMs in the places designated in the Elevation Library Manager. This means the Session Log will report only any unexpected cases that are not included below.
Errors and unusable raster files only This option has the Session Log report the names of any DEMs or raster files without elevation information that were not added to the Library. Any errors are also reported.
Errors, unusable raster files and skipped (non-raster) files This option has the Session Log report the names of any DEMs or raster files without elevation information that were not added to the Library, plus report the names of any non-raster files such as .rrd, .aux, .txt and so forth that were not added to the Library. Any errors are also reported.
Errors and images added to elevation library only This option has the Session Log report the names of the images successfully added to your library to ensure you have added all the files that you need. Any errors are also reported.
Errors and all directories and images scanned This option has the Session Log report the names of all directories and images that were scanned for possible use in the Library. Any errors are also reported.
All messages Select this option to see both the specific files added and the specific files not added. Any errors are also reported.
Example of Session Log Report
OK Click to run the file requirements process and close this dialog.
Cancel Click to cancel any changes made and close this dialog.
Help Click to open this On-Line Help document.
Using the Elevation Library
Once it has been created, the Elevation Library can be used like any regular file for specifying the height data to be used for orthorectifying imagery. It will also support generating terrain-corrected point measurements and features as well as more accurate display of georeferenced data over the image.
For example, to improve accuracy when using the RPC model automatically associated with a NITF image, open Image Info dialog and select Set Elevation Source. In the Elevation Source dialog, you can select Elevation Library rather than a specific file or the default constant elevation specified in the image header metadata.
Preference to Automatically Use Elevation Library
For those with access to NITF or TFRD imagery that ERDAS IMAGINE auto-associates with the embedded 3D geometric model, or if the imagery has been pe-calibrated with a 3D sensor model; you can turn on a Preference so that the sensor model automatically uses the Elevation Library rather than manually setting the elevation source.
This preference is set in the Elevation Library preference category in the Preference Editor and is called Sensor models should auto-associate. The preference is set to Off by default.
In both the auto-association and manual association cases, note that there are some cases (particularly where a grid-based vertical datum transformation is required to match the elevation data to the 3D sensor model parameters) that will result in degradation of image display and roam performance when using the orthorectification on-the-fly capabilities of the ERDAS IMAGINE Views.
Total count of files added to Library