IMG

ENVI, ERDAS, IDRISI and IMDISP .img formats. Manifold autodetects and configures the right dataport.  

 

When linking ERDAS IMG file ensembles that include intermediate levels in the RRD (Reduced Resolution Dataset) file, Manifold will automatically use those intermediate levels to provide very fast display.  This topic uses ERDAS IMG files as an example.  The data set used is the 1.1 gigabyte NLCD 2011 Land cover data zipfile downloaded from the US government's https://www.mrlc.gov/nlcd11_data.php web page.

Linking

In Manifold we can take advantage of intermediate levels already stored within an .img file's .rrd file. that by linking an ERDAS .img file into our project.   The link creates a data source cylinder that indicates the data is stored outside of the project, in the original IMGfile.  When we expand the data source we can see the image within and then we can use that image as a layer in maps.  This works well in cases when we only intend to view the image and not to edit it.

 

Important: When linking an IMG file the image that appears in that data source in the Manifold project stays resident in the IMG file ensemble.   It is an IMG image even though it appears in many respects, for the convenience of the user, to be a Manifold image.  

 

To link an IMG format file:

 

  1. Choose File-Link from the main menu.

  2. In the Link dialog browse to the folder containing data of interest.

  3. Click the .img file desired.

  4. Check or uncheck the Save cache box as desired.

  5. Press Link.  A linked data source will appear in the project.

  6. Press the + icon next to the data source to expand the data source to see the image it contains.

 

dlg_link_img_erdas.png

 

Unzipping a typical archive that contains an ERDAS IMG file will create a variety of files.  The .img is the one we choose as it contains all the pointers required to load the image from the other files.   

 

The Save cache box allows setting cache options.

 

dlg_link_ecw02.png

 

Checking the Save cache box will create a .MAPCACHE file in the destination folder, which can speed up later use.   We click Link.

 

il_link_img_erdas01_01.png

 

That creates a data source that contains an image and the image's table in our project.  The data source has an asterisk * character in the data cylinder icon because we have not yet saved the project.  

 

We can double-click on the image to open it.   ERDAS .img files linked into a project will normally open instantly because they will have intermediate levels stored in the associated .rrd file.

 

il_link_img_erdas01_02.png

 

ERDAS IMG files can provide projection information.   If a particular file does not, we can manually specify projection information by launching Assign Initial Coordinate System in the Component pane.

Import

When we want to do more than just viewing, and to work with images using the full power of Manifold, we can import an IMG as a Manifold image.  

 

Importing an IMG into Manifold and opening it the very first time will usually be much slower than linking the image because Manifold will generate intermediate levels.  Saving the project the first time also will be slower.  But that is a one-time task and after we save the project as a .map file thereafter opening the .map project and opening the image will be very fast.

 

Important: When importing an IMG file the image that appears in the Manifold project is a native Manifold image with no further connection to the IMG file from which it was imported.   It is a native Manifold image and no longer is an IMG image.  

 

To import from IMG format:

 

  1. Choose File-Import from the main menu.

  2. In the Import dialog browse to the folder containing data of interest.

  3. Double-click the .img file desired.

  4. An image and the image's table will be created in the project.  

 

Notes

Exporting and intermediate levels - To save space, exporting a big image to ERDAS IMG skips producing data for intermediate level 1, and instead produces intermediate levels starting from level 2 to save space.

See Also

Assign Initial Coordinate System