Raster File Format Handling

Being the principal module in MicroStation for attaching rasters, Raster Manager is able to open and display more than 30 file formats of any size, and is only limited to RAM memory capacity.

File Formats

Raster Manager supports many geospatial enabled as well as non geospatial file formats.

Proprietary File Formats

The Raster Manager also supports four proprietary file formats that were designed to ensure maximum performance for visualization and the editing with Bentley Descartes:

• HMR - The HMR file format is the first proprietary file format that was developed and supports only 2 or 256 colors.  This format has been replaced by the iTIFF file format.

• iTIFF - The iTIFF file format was developed to replace the HMR file format. Its most important advantage over the HMR file format is its support for 24 bits RGB and 32 bits RGBA color space.

Performance tip : To improve performance when working with images in Raster Manager or Descartes, consider converting old HMR files to iTIFF. 

• cTIFF - The cTIFF file format is very similar to the iTIFF file format but it is used as a cache file format.  The cTIFF file format cannot be created or attached directly in Raster Manager.  Instead,  it's created and used when needed which is determined by the original file format, the cache settings and on-the-fly transformation of the attached image.  

• iTIFF64 - This is the latest proprietary file format that uses an internal 64-bit pointer for the indexing the raster data.  This allows the creation of files that exceed 4 gigabytes in size.  

Supported File Formats

Raster Manager supports dozens of different file formats, which are listed in the table below.

* R: Read,  W: Write, C: Create

** C: Can store DEM as well as imagery , O:  Can only store DEM data

Tip:  For the most current list of supported input and output file types, please refer to MicroStation's Help > Supported Input File Formats and Help > Supported Output File Formats.

File Open Options

Raster Manager offers a variety of options that can be specified during the attachment of an image. Those options can be set on the Raster Attachment Options dialog, which is shown only when Open Settings Dialog is checked on the Attach Raster Reference dialog. The Raster Attachment Options dialog is shown below.

Attachments 

The top pane displays a list of rasters that were selected in the Attach Raster Reference dialog. In the above example, the list contains two files: SinglePage.bmp and MultiPages.gif.   The attachment options are then applied to the selected file(s).  

Note that the icon for a multi-page image differs than that for a single page image.   As its name implies, a multi-page image contains multiple images.  To choose the correct image to display in a multi-page image, right click the selected file entry and choose Page Selection. 

Display Print

The Display Print pane contains options related to the visual appearance of the raster to be attached.

• Views: Specifies which of the eight MicroStation views the raster is going to be visible.
• Plane: One of the three planes to put the raster on. Background places the image behind all vector graphics.  Foreground places the image in front of all vector graphics. That is also valid in a 3D model. For example,  when working with a 3D model, a raster that's put on the Background plane is going to lie behind all elements, even if the raster is closer to the camera than the elements. If the image is to appear in front of elements that are farther from the camera, then the image should be put on the Design plane.
• Print: Specifies if the raster is printable or not.
• Print Gamma and Display Gamma: Sets the gamma value for printing and display.
• Clip: Specifies if the clip is going to be applied when the raster is displayed. Note:  Aside from iTIFF and iTIFF64, a raster cannot have a clip when it's first attached since other formats don't support the saving of a clip.  However, after being attached a clip can be subsequently set and saved with the attachment.

General

The general pane contains the following options to apply to the attachment: 

• Level: The level the raster will be placed on.
• Color: The color of the raster's border.
• Line Style: The line style of the raster's border.
• Weight: The weight of the raster's border.
• Class: Specifies the element class.
• Priority: Specifies the display priority.

Image 

• Logical Name: A unique logical name given to the raster.
• Description: A description of the raster.

Color

The color pane contains options that affect the visual appearance of the raster. Note that the original data in the raster are not modified, only its on-screen appearance is affected.

• Tint: Defines the tint to apply to the image..  
• Contrast: Sets the display contrast setting of the image. This is similar to changing the contrast of a monitor.
• Brightness: Sets the display brightness of the raster. This is like changing the brightness of a monitor.
• Invert: If set, this inverts the image meaning black pixels become white and white pixels become black.
• Transparency: Specifies which pixel colours will be transparent. 

Geometry

The Geometry pane contains an option related to the localization of the raster.

• Geo Priority: This specifies if geo-coding and georeferencing will be coming from the information stored in the raster element (Attachment) or in the raster file (Raster Header). The Raster Header option is only present if the format of the selected file supports the saving of  geo-coding and georeferenced information.  For more information, refer to Supported Input File Formats.   

Action

The Action pane contains an option related to the placement of raster.

• Place Interactively: When this option is enabled, the raster can be attached by entering a pair of diagonal datapoints to define the extents of the image. 

Extended

This pane contains an option related to the snapping of raster.

• Snappable: This option specifies if the raster is snappable or not. 

File Format Details

Visualization

Raster Manager uses a different strategies to display very large images smooth, fast and with limited, configurable memory usage. Those strategies are: on-demand access, RAM caching, file improvement (caching) and independent viewing process.

On-Demand Access

When an image is attached in Raster Manager its data is not automatically loaded in memory.

Raster Manager starts loading the raster data only when the image becomes visible on at least one view. It then loads the portion of the raster that's visible and only at the resolution that best fits the current view's resolution in units per screen pixel.

This on-demand access capability of Raster Manager allows the attachment of  images that are several gigabytes in size  completely independent of the available RAM capacity.

RAM Caching

Raster Manager has a memory pool that's used to store the most recently requested raster's data.  This information is stored as a tile which is a square bitmap. This allows fast access to raster data that has been recently accessed.

Cache File

The on-demand access and RAM caching strategies explained above are only optimal when the raster data is stored as tiles and sub-resolutions in the raster file.  

Unfortunately, not all file formats support the storing of raster data as tiles and of sub-resolutions.  Also, some file formats support a few different storing strategies and the selected storing strategy during the creation of the raster file might not be optimized for Raster Manager.  For example, a TIFF raster file with no sub-resolutions and with raster data stored as separate lines. 

The two examples below illustrate this.

Example 1 :

Example 2 :

To ensure the optimization of the on-demand access and RAM caching, Raster Manager creates cache files (*.cTIFF) in a temporary folder for those file formats that do not have tiles or sub-resolutions already defined.

For example, when attaching a TIFF file, no cache is present and must therefore be generated.  This will result in a lengthy  redisplay, however, for each zoom operation, a "snap shot" is added to a locally cached file which is then utilized in subsequent viewing operations. As you work with the file, caches will be created and re-used which results in display speeds and improved performance over time.

Performance Tip:  For optimal display speeds, Bentley's own iTIFF format can be used; it already contains the required sub-representations for high performance display.

Cache Manager

The Cache Manager dialog can be used to configure file caching.

• Delete cache file on exit: When checked, all cache files created during the session are deleted when MicroStation is closed. 
• Delete cache files older than: When checked, all cache files older than a specified number of days are deleted when clicking the Run Now button.
• Limit disk space usage to: When checked, the space usage attributed to the cache is limited to the amount specified.
• New location: Specifies the location of the cache files.

Performance can be influenced by the location of the cache files. For example, if the Cache Manager is configured to use a network drive rather than a local drive, it may impede performance.

In addition to the Cache Manager, the Load Mode sets how memory management for raster will be handled. The options for this can be found in WorkSpace > Preferences > Raster Manager > Memory.  MicroStation  V8i also  provides an option to tune the memory usage by a % factor of the memory you have available on your machine.

Independent Raster Display

The last visualization strategy that Raster Manager is using is to display images using an independent.  This is also called progressive display or non-blocking raster display and is set in Workspace > Preferences > Raster Manager > General.

Displaying rasters using an independent process removes jerky panning and zooming that can be caused when viewing raster data stored remotely on a server.  Raster Manager - Server Streaming Raster Visualization  This undesired behaviour can also occur when locally stored raster visualization consumes excessive CPU power.

When viewing rasters using an independent process, the raster data is only sent to MicroStation when it becomes available.  When zooming in on the image, Raster Manager will display stretched, lower resolution raster data until the higher resolution data arrives.  This results in a progressive display.