Another raster bulletin, and quite an important one....
Safe Software raster development has added new raster processing to
our flagship FME product. The RasterMosaic Factory and its
corresponding RasterMosaicker transformer are now available in the FME
UT and in Workbench. A new documentation chapter has been added to
assist our users in understanding this new processing.
Overview:
This factory can be used to mosaic a collection of input raster
features into a single raster feature. All collective properties of
the input raster features together determine the georeferencing
information on the output mosaicked raster. The RasterMosaicker
supports both selection and multiple bands per raster. The factory can
also automatically snap and resample on the second and following
raster features if the features do not correspond well to the position
of the first raster feature. Snapping will occur if the rasters do not
lie in the same grid, and resampling will occur if the rasters have
different spacing or resolution.
The selected bands with the same interpretation are removed from the
input features and mosaicked to form a new band in the single output
raster feature. The first selected bands from each input raster form
the first new band in the output, and the second selected bands form
the second new band, and so on. The unselected bands are ignored and
will not be available in the mosaicked raster. The order of the input
features determines the layering effect of the input raster features
as the first feature may be covered by the second feature, and the
second feature may be covered by the third feature, etc. if later
raster features overlap earlier ones.
Options:
In this release, five options are available.
The GROUP_BY option can be used to partition raster features into
groups based on some attribute values, and then the factory will
produce one mosaicked raster feature for each group. The default is
not to group by any attributes.
The COUNT_ATTRIBUTE option adds a new attribute to each output raster
feature to record the number of input raster features processed. The
default is not to add a count attribute.
The ACCUMULATE_ATTRIBUTES option sets the mosaicked raster to either
merge all the attributes from the input raster features or ignore all
the attributes. The default is `Yes'.
The NODATA_OVERWRITE option determines whether a nodata value on top
can overwrite a real data value underneath in an overlapped area of
two rasters. The default is `No'.
The INTERPOLATION_NAME option determines which interpolation kernel to
use in case of snapping and/or resampling. The default is `Nearest
Neighbor'.
The RasterMosaic Factory is now available in the recent FME 2007 betas
as of build 4323+ (20070316).
FAQ:
Q1) Does the RasterMosaicker work on any raster features?
A1) The RasterMosaicker has the following limitations for the input
raster features:
- the same coordinate system
- the same number of selected bands
- the same nodata value in each band
- the same number of palettes per band
- at most one palette per band
- the same band and/or the palette interpretations in each set
of selected bands
The limitations seem to be very strict; nonetheless, many other raster
factories and functions ease the use of the mosaicker.
Q2) What improvements are planned for this factory in the future?
A2) This factory may have improved functionality and options in future
releases. For example, the mosaicker may be able to combine
overlapping areas in more ways and may take a new attribute from each
input raster feature to determine the
transparency/opacity/blending-ratio of the data values in the
overlapped area. There can also be different blend modes, such as
difference and exclusion.
Q3) Is this supposed to replace mosaicking functionality in the
database formats (For a example in SDE and in the future Oracle)?
A3) No. This factory can provide an alternative to the existing
database mosaicking functionality within database writers, but it was
intended as a general solution that would include mosaicking of any
suitable raster formats within FME including file-based formats like
GeoTIFF or JPEG2000. Often if a database is the destination format it
is more efficient to use the native mosaicking capabilities of the
database.
For insights into what's up at Safe Software and what's on the development
horizon, visit Safe's blog at spatial-etl.blogspot.com.
Safe Software has also made slides available that outline enhancements planned
for FME 2007. The slides are from the "Road Ahead" presentation given on Day 2
of the FME Worldwide Users Conference. To view these slides, visit
www.safe.com/2006uc.
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