Blue Marble’s Geographic Transformer is an image
referencing, reprojection, mosaic creation and compression tool. Based
on the company’s core coordinate conversion technology, Blue Marble
entices users to “Master Raster” with this powerful yet easy-to-use
package. As with the rest of Blue Marble’s products, the Geographic
Transformer is designed to handle a small number of useful tasks and
handle them very well.
Formats
As one might expect, Geographic Transformer supports all major import
and export formats, and is the only product available today that
supports read and write of all the major wavelet compression formats
(JPEG2000, ECW and MrSID). Input formats include TIFF/GeoTIFF, BMP,
JPEG, JPEG2000, PNG, BSB Chart v3, ADRG, MrSID, ECW, CADRG, DOQQ, BIL
and BSQ. Output formats include TIFF/GeoTIFF, BMP, JPEG, JPEG2000, ECW,
MrSID and PNG. ECW and JPEG2000 compression formats are fully supported
within the base product, but output to LizardTech’s MrSID format
requires the purchase of an additional “data cartridge” from the
company.
Referencing
The Reference tab allows users to input source coordinates and reference
coordinates by entering them manually, clicking on source and reference
imagery, or by importing from MapInfo TAB, ADRG GEN, ER Mapper ERS or
World Files. The reference image viewer can also open ESRI Shapefiles,
MapInfo MIF and TAB, AutoCAD DXF and DWG, or MicroStation DGN files.
Registration point coordinates are displayed in the main window, along
with X, Y and XY error. Forward and reverse residuals and root mean
square error values are displayed at the bottom, and an error plot can
be generated to visualize error distribution. There’s also an option in
the user preferences to flag any errors greater than a specified
threshold value when viewed in the error plot. Supported transformation
models include Affine, First-Order Polynomial and Second-Order
Polynomial.
Transformations
The Transform tab lets users choose source and destination files,
along with input and output coordinate systems. The area to be
transformed is explicitly defined using image extents, reference
point extents or a user-specified rectangle denoted with upper-left
and lower-right corner coordinates. Output pixel size can be
explicitly defined, or the software can compute the optimum size
automatically. Resampling options found in the user preferences
include Nearest Neighbor, Bilinear Interpolation, Quadratic
Interpolation and Cubic Convolution.
A useful option is the ability to output the results of the
transformation as a series of image tiles, either in 1.5-minute
sections or in a user-specified row-column tiling structure. The
user has control over the size of the tiles (in either pixels or
coordinate system units) and control of the starting point for the
tiles. Transformations, even between different datums, are quick to
process and output. Tests using a 150MB RGB image in GeoTIFF format
resulted in an elapsed time of about 8 seconds to transform between
UTM, NAD83 meters to State Plane, NAD27 U.S. feet using a
second-order polynomial transformation model (2.8 GHz processor, 2GB
RAM).
In addition, transformations can be accomplished in batch mode,
applying the same referencing and transformation settings to
multiple images. The ability to easily batch process multiple images
is a major plus for users working with a large number of images.
Automatic output file naming, using a prefix or suffix appended to
the original file name, simplifies the task of generating the batch
input settings. Transformation file settings also can be saved for
future use or to be used as a template for other transformations.
A
large number of coordinate system definitions, datum
definitions and ellipsoid definitions are available for use in
the Geographic Transformer. The availability of coordinate
systems from across the globe makes the software useful in any
geographic extent. Datum definitions include more recent
definitions often overlooked by other software packages, such
as HARN-based datums for state plane systems. In addition, the
ability to create custom datum, ellipsoid and coordinate
system definitions is included.
Mosaics
Simple image mosaics can be created from up to 256 individual
images that share the same coordinate system, resolution and
color palette. Images are added to the mosaic in the order
they appear in the mosaic list (i.e., If not A then B, else
A). Background color of the images (null values) can only be
defined as black or white. The ability to create and/or use
“stitch lines” or custom mosaic boundaries for each image
isn’t included and would be a welcome addition. For simple
mosaics, though, processing is efficient and effective.
Compression
Geographic Transformer doesn’t offer a “Compress” tab to
perform simple image compression, but the major compression
formats are available as output options from the transform and
mosaic tools. A compression tab would be a nice addition, as
the functionality to compress is already included in the
software. Changing the desired compression ratio (for all
three formats at once) entails a quick change in the software
preferences. There’s also an option to enable/disable lossy
compression for JPEG and Packbits compression for TIFF.
The Geographic Transformer performs a limited set of useful
tasks, and performs them in an efficient, user-friendly
manner. A simple, user-friendly interface allows easy access
to all of the program’s tools and options, and a Getting
Started guide and “walk-through” wizards are helpful and well
written. The variety of supported input formats, output
compression formats, and coordinate systems make the program
valuable and applicable for users working with large or small
imagery files anywhere in the world.
