About working with an image service in MicroStation

On the MicroStation Image Server client dialog box, you can change the order in which the image services appear, remove image services, set the image service properties, zoom to view the overview of image services, use the viewpoint functionality, and autorefresh image services.

Some of the image service properties are set by the image service administrator; however, there are many properties that you can alter. These properties include the spatial reference information, default sampling method, mosaic method, compression method, and background color. The image service administrator can also control what properties the client can choose to alter. For example, you may not always get to choose the Viewpoint mosaic method because there are limited data sources this method can be used with, and the administrator can remove it from the choices given to the client.

The image service properties

Field	Description
Spatial Reference System	Defines the spatial reference system based on which imagery should be displayed. Each request to the server is for an image based on a rectangular window in the specified spatial reference. Some client applications can define or redefine the required spatial reference.
Sampling Method	Defines the sampling method by which raster pixels are sampled by the server to match the resolution of the client request. Depending on the application, the sampling method can be changed. More accurate radiometry values are obtained using the nearest neighbor sampling but can result in jagged edges of features. Bilinear interpolation provides smoother images but can result in some smoothing of the image.
Mosaic Method	An image returned to the client can be created from a number of input rasters. The mosaic method defines how the mosaic is created from different rasters. Closest to Center—Enables rasters to be sorted based on a default order where rasters that have their center closest to the view center are placed on top Closest to Nadir—Enables rasters to be sorted by the distance between the nadir position and view center;similar to the Closest to Center but uses the nadir point to a raster, which may be different than the center, especially for oblique imagery Closest to Viewpoint—Orders rasters based on a user-defined location and nadir location for the rasters using the Viewpoint tool By Attribute—Enables the ordering of rasters based on a metadata attribute defined in a field and the difference from a base value Most Northwest—Enables raster ordering in a view- independent way, where rasters with their center most northwest are displayed on top Seamline—Cuts the raster using the predefined seamline shape for each raster using optional feathering along the seams Lock Raster—Enables a user to lock the display of a single or multiple rasters based on an ID or name
Lock Raster ID	The image is locked to a specified raster ID if the mosaic method is defined as Lock Image. This can be used to display by default only one raster in a service. The raster ID is specified in the service table. If you know the ID of the raster you want to lock, you can enter it in the service table. Refer to step 9 in Viewing image service metadata in MicroStation to learn about locking rasters.
Compression Method	Defines the method of compression in which to transmit the mosaicked raster data from the server to the client. If accessing the image services over a LAN, large data volumes do not cause a problem. However, when working over slower connections on the Internet, it is better to apply a compression to the imagery before transmission. This compression reduces the size of transmitted imagery but puts an additional load on the service provider to compress the data first. Uncompressed results in no compression being applied to the imagery, providing the highest quality, but results in the maximum data transfer across the network. JPEG compression is an efficient compression method that can often compress imagery by about three to eight times with little degradation in the image quality. JPEG 2000 is waveletbased, which provides high compression ratios (8–15) with little degradation in the image quality but only when the size of the transmitted image is large. For small screen-sized requests, JPEG is generally better. JPEG 2000 also puts a heavier load on the service provider. LZ77 is an efficient lossless compression method that is primarily for imagery with similar pixels, such as scanned maps or results of classifications.
Compression Quality	Defines the quality of compression. A compression quality of 100% is the best. Values closer to 0 have very high compression ratios with little regard for quality. Values closer to 100 maintain visual quality while attempting to compress the image. A value of 100 may also indicate no loss in quality if using a lossless compression.
Background Color	Defines the default background color of the image service. Where there is no imagery, the specified color value is displayed.

Image service properties