Source mosaic datasets

If the input metadata table includes a mix of imagery (possibly from different sensors), it is recommended that the different image collections be loaded into separate source mosaics for the first stage of data management. One source mosaic is recommended for each logical group (for example, by year or by sensor, whichever is appropriate).

During incorporation, the data files can be selected from the existing metadata table using a query. The query string may be a file name filter (abc*.tif) or a query (for example, sensor='ETM' and year='2004'). Doing this allows the data combination process to be carefully controlled and enables parameters to be defined prior to compiling the source mosaic datasets into the derived mosaic dataset.

Catalogs of browse images can be very large and may contain millions of images. The Table raster type in ArcGIS does not utilize parallel processing, so one way to speed up the combination of very large databases is to split the database physically (or virtually, using a query) into subsets and add rasters for each subset in parallel, using separate source mosaic datasets.

Creating a new mosaic dataset

It is typically recommended to set the coordinate system for each source mosaic dataset to WGS_1984_Web_Mercator_Auxiliary_Sphere. This is because oftentimes the source data can be stored in individual local coordinate systems (for example, multiple UTM zones), and the coordinate system for the mosaic dataset should support the maximum extent expected for all imagery.

Adding rasters

This workflow assumes a feature table is available and that the Table raster type will be used to combine browse imagery into the source mosaic dataset. The advantage of using the Table raster type is that the metadata is immediately imported into the attribute table.

Note:

The sensor raster types (for example, Landsat, Quickbird, and so on) should not be used, as they are designed for combining the full-resolution datasets into a mosaic dataset and not the browse imagery. It is recommended that you not invoke Update Overviews when creating source mosaic datasets; see further considerations on creating Overviews.

Metadata

Metadata should be populated when adding data into the source mosaic dataset. When using the Table raster type, all metadata from the input table will be added into the attribute table of the mosaic dataset. Any required field names and types will be automatically created. Ensure nonrequired fields areremoved first. To use the Table raster type, see ArcGIS Help 10.1.

There may be a need to add additional metadata separately after the source mosaic dataset has been populated with data. For example, if multiple source mosaic datasets are required to accommodate different data collections, a field named Dataset_ID is recommended to identify all records according to their source mosaic dataset (based on a single collection). When the source mosaic datasets are later merged into the derived mosaic dataset, this field will be necessary to allow queries to identify the original collection.

Custom metadata fields must be added to the mosaic dataset attribute table before attempting to populate those fields with metadata.

Calculating cell sizes

When adding rasters to a source mosaic dataset, the option to update cell size ranges should be set to off. If this is set to on, the system attempts to perform an analysis of the overlapping imagery to determine the appropriate pixels and potential overlap between images. It is much faster to turn this off and use the Calculate Field tool to set the MinPS and MaxPS. The MinPS should be set to 0 and the MaxPS to a value that corresponds to the average image width of 300. This results in the image being displayed until a scale is reached where it covers less than one-third of the screen display.

Calculating footprints

For the browse imagery workflow, the input metadata table should define the footprint (valid image extents) of each image. If True, when images are combined using the Table raster type, the footprint will be defined. Note that if the images are rectified with projections that are different from the Source Mosaic Dataset, it will be necessary to reproject these footprints so they are all in the correct SRS (spatial reference system). If reprojecting the data, care should be taken to review the density of vertices in the resulting footprints. Typically, a minimal number of vertices should be used or the resulting feature class can become unnecessarily large.

If an accurate footprint does not exist, then by default, the system will use the envelope (full extent) of the image file as the footprint. In the case of rectified imagery noted above, if the browse image is stored in a projected coordinate system, this is unsuitable, and it will be necessary to run the Build Footprints tool. If NoData exists within the image files (that is, it has black or white borders), use the RADIOMETRY computation method, taking care to exclude data values that may be similar to the NoData value. For example, assuming the browse images are compressed as JPEGs, and 0 is used for NoData, set the minimum data value to 3 to eliminate compression artifacts that have altered the NoData values. To speed up the process, reduce the Request size to a minimum value (for example, the average number of columns should be 1,000). Also, set the number of vertices to a lower number, such as eight.

If the images are nonrectified and will be georeferenced using an AUX.xml file, the footprints should be correct by default when set to the full extent of the image file. If not, footprints can be quickly computed by running the Build Footprints tool, using the GEOMETRY computation method. In this case, set the number of vertices to four.

In both cases, it is best to test this on sample imagery that includes an image as the boundaries of the expected extent.

Note:

Since the number of browse images is typically very large, running the Build Footprints tool can take a substantial amount of time. It is strongly recommended that the image extents be known at the time of adding data and that the prebuilt extents are used to define the footprints.

Building a boundary

After adding the data to the source mosaic dataset, run the Build Boundary tool with the method set to ENVELOPE. This will ensure that the envelope of the image footprint is used to create the boundary. By using this method, the boundary is uncomplicated and will require the least number of vertices. This is important when the volume of data is large.

Mosaic dataset properties

The default values do not need to be changed for the properties of the source mosaic datasets, as it is generally used only for quality assurance purposes. Properties will be addressed for the derived mosaic dataset.