You are here: Creating and Maintaining Catalogs > Setting a Catalog's Advanced Properties

Setting a Catalog's Advanced Properties

The advanced properties of a catalog are:

Changing Download Policy

You can determine whether or not you want to allow users to download the file from which they are viewing scenes in Express Server. This can be done globally on the Settings page, or you can set policy for a particular catalog. Any per-catalog policy overrides the global setting for that catalog.

By default, files are not downloadable.

To remove the file-download restriction for a catalog:

  1. Open the Express Server Manager (see Accessing the Express Server Manager).
  2. Click Catalogs on the top navigation bar, then select a catalog in the list.
  3. Select Advanced on the left-hand navigation panel, then click Edit.
  4. Select the Allow item download checkbox, then click Save.
  5. If you have no further settings to edit, click Publish.

Remember that clicking Save in the workspace only temporarily saves your changes until you click Publish or Discard. Clicking Publish sends all edits on all the configuration pages to the live Express Server. Clicking Discard overwrites all pages of the workspace with the current live configuration.

Changing Tile Browsing Policy

You can determine whether or not users can browse the individual tiles making up a spatially indexed catalog. This can be done globally on the Settings page, or you can set policy for a particular catalog. Any per-catalog policy overrides the global setting for that catalog.

By default, tile browsing is allowed.

To restrict tile browsing for a catalog:

  1. Open the Express Server Manager (see Accessing the Express Server Manager).
  2. Click Catalogs on the top navigation bar, then select a catalog in the list.
  3. Select Advanced on the left-hand navigation panel, then click Edit.
  4. Select the Disallow tile browsing checkbox, then click Save.
  5. If you have no further settings to edit, click Publish.

Using Black No-Data

If you create an image catalog from imagery that does not have transparency values configured, you may want to default to rendering black pixels as no-data. Black pixels in the image will display as transparent.

To use black no-data:

  1. Open the Express Server Manager (see Accessing the Express Server Manager).
  2. Click Catalogs on the top navigation bar, then select a catalog in the list.
  3. Select Advanced on the left-hand navigation panel, then click Edit.
  4. Select the Use black no-data checkbox, then click Save.
  5. If you have no further settings to edit, click Publish.

NOTE: To create image mosaics with transparency between image tiles, either select the option to use black no-data or ensure that the tiles in the image mosaic have transparency configured.

Setting Dynamic Range

The Dynamic Range property limits the dynamic range of an image requested from Express Server. This is particularly useful for images that only use a small portion of their datatype bandwidth. For example, 11-bit images are often stored as 16-bit images, with the upper five bits left empty; only the first 11 bits are meaningful. For an 11-bit image, the minimum value would be 0 and the maximum value would be 2047 (211 - 1).

Setting the dynamic range does not change the pixel data of an image; it only gives a suggestion as to how the image should be displayed. Some applications may honor these values and some may ignore them.

To set a per-catalog dynamic range:

  1. Open the Express Server Manager (see Accessing the Express Server Manager).
  2. Click Catalogs the top navigation bar, then select a catalog in the list.
  3. Select Advanced on the left-hand navigation panel, then click Edit.
  4. Enter minimum and maximum values in the Dynamic Range fields, then click Save.
  5. If you have no further settings to edit, click Publish.

Setting Size Constraint

The Size Constraint property limits the size of an image requested from Express Server. This is useful for controlling server load and limit access to high-quality image data. Setting a size constraint can be done globally on the Settings page, or you can set a value for a particular catalog or catalog group. Any per-catalog or per-group setting overrides the global setting for that catalog or catalog group.

By default no limit is enforced.

To set a per-catalog size constraint:

  1. Open the Express Server Manager (see Accessing the Express Server Manager).
  2. Click Catalogs or Catalog Groups on the top navigation bar, then select a catalog or a catalog group in the list.
  3. Select Advanced on the left-hand navigation panel, then click Edit.
  4. Enter width and height values in the Size Constraint fields, then click Save.
  5. If you have no further settings to edit, click Publish.

Adding Custom Properties to a Catalog

You can add custom properties globally on the Settings page or add them to individual catalogs. Any per-catalog custom properties created override any global custom properties.

To add custom properties to an individual catalog:

  1. Open the Express Server Manager (see Accessing the Express Server Manager).
  2. Click Catalogs on the top navigation bar, then select a catalog in the list.
  3. Select Advanced on the left-hand navigation panel, then click Edit.
  4. Enter a name and a value and click Add. The property is added to the table.
  5. Repeat to create additional properties, then click Save.
  6. If you have no further settings to edit, click Publish.

Setting Buffer Merge Rule

When two images overlap in the creation of a mosaic for delivery, Express Server’s mosaicker must choose between the top or bottom pixel. It might seem obvious that the top pixel should be used if its value does not equal the no-data value, but because lossy compression may introduce slight changes in the values of the no-data pixels, some extra care is required to avoid mistaking these “drifted” no-data values for valid image data and thus to reduce tile boundary artifacts.

For example a black pixel, which has the sample values 0,0,0, may end up being 0,0,1 or 0,1,0 after compression, which will still look black to the eye but not to the mosaicker. The mosaicker, in seeking out true black pixels to make transparent, treats this as valid image data instead and writes it to the output image, introducing a near-black pixel instead of the correct one from the other tile, an effect that when multiplied along a boundary or around the collar of an image is called speckling.

The buffer merge rule is helpful here because it enables flexibility in what is otherwise a hard rule. The rule specifies how the mosaicker determines which pixel to use as the output pixel. One rule is better for images compressed losslessly and the other is better for images that have been compressed lossily.

The better rule for images that were lossily compressed is “Fuzzy”. The Fuzzy method establishes a spherical zone of “fuzziness” around a given top pixel value (think of the R, G and B color values as values on the X, Y and Z axes of a three-dimensional graph). If the pixel value falls within that zone it is treated as the no-data value and will be transparent; that is, discarded in favor of the bottom pixel. This allows you to “rope in” those drifted no-data values. The Fuzzy rule requires the specification of a Fuzziness value.

For losslessly compressed images there is no danger of mistaking the no-data, since the pixel values remain bit-for-bit identical to those of the source image and thus cannot have drifted. In this case the buffer merge rule should be “Strict”. The top pixel is then always used unless it exactly matches the no-data value.

You can set a buffer merge rule globally on the Settings page, or you can set the rule for individual catalogs or catalog groups. Any per-catalog or per-group rule overrides the global setting for that catalog or catalog group.

By default the buffer merge rule is Fuzzy and the Fuzziness value is 3.

To change the buffer merge rule:

  1. Open the Express Server Manager (see Accessing the Express Server Manager).
  2. Click Catalogs or Catalog Groups on the top navigation bar, then select a catalog or a catalog group in the list.
  3. Select Advanced on the left-hand navigation panel, then click Edit.
  4. Select the radio button for the rule you wish to activate.
  5. Move the Fuzziness slider to specify a positive integer between 0 and 20, then click Save.
  6. If you have no further settings to edit, click Publish.

Specifying Watermark File Name

You can specify a MrSID image to be used as a watermark that is overlaid on top of all images in a catalog. This can be done globally on the Settings page, or you can specify a watermark for a particular catalog or catalog group. Any per-catalog or per-group setting overrides the global setting for that catalog or catalog group.

Any image used as a watermark must be located in the directory <Express Server installation directory>/ImageServer/etc/watermarks.

By default no watermark is specified.

To specify a watermark image for a catalog:

  1. Open the Express Server Manager (see Accessing the Express Server Manager).
  2. Click Catalogs on the top navigation bar, then select a catalog in the list.
  3. Select Advanced on the left-hand navigation panel, then click Edit.
  4. Select an image from the Watermark File Name drop-down menu, then click Save.
  5. If you have no further settings to edit, click Publish.

NOTE: Watermarks do not appear in thumbnail images.

Setting Thumbnail Definitions

Thumbnail definitions control the size of thumbnail images produced by Express Server in response to thumbnail requests. Express Server has three built-in thumbnail definitions: small (32 x 32), medium (64 x 64) and large (128 x 128). In addition there are two configurable defaults: main (80 x 50) and gallery (200 x 220).

The thumbnail output format is JPEG.

You can set thumbnail definitions globally on the Settings page, or you can set them for a particular catalog or catalog group. Any per-catalog or per-group setting overrides the global setting for that catalog or catalog group.

To set per-catalog thumbnail definitions:

  1. Open the Express Server Manager (see Accessing the Express Server Manager).
  2. Click Catalogs or Catalog Groups on the top navigation bar, then select a catalog or a catalog group in the list.
  3. Select Advanced on the left-hand navigation panel, then click Edit.
  4. Edit existing entries or click Add and enter a new one, then click Save.
  5. If you have no further settings to edit, click Publish.