Product
Information
Vendor:
PCI Geomatics
50 West Wilmot Street
Richmond Hill, Ontario
Canada, L4B 1M5
905-764-0614
905-764-9604 (fax)
info@pcigeomatics.com
System Requirements:
For Windows 95/98/2000 and NT version
4.0
Processor:
Pentium, Pentium MMX, Pentium Pro,
Pentium II or Pentium III
Memory:
Minimum 32 Mb RAM, recommend 64+
Mb
Disc Space:
40-50 MB required for Installation
Software is also available in Unix and Linux
versions.
Cost:
OrthoEngine Core (required) $2,000
USD
OrthoEngine Airphoto Edition $3,000 USD
OrthoEngine Sensor Rectification Edition
$3,000 USD
OrthoEngine IKONOS Edition
$3,000 USD
OrthoEngine 3D Viewing and Editing $3,500 USD
OrthoEngine Automatic DEM $4,000 USD
OrthoEngine Automatic RADARSAT DEM $4,000 USD
Note: prices are for PC platform
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Summary
OrthoEngine software, produced by PCI Geomatics of Richmond Hill,
Ontario, is a comprehensive suite of products designed for
performing the tasks required in producing high quality, seamless
digital orthophoto imagery products from aerial (standard and
digital) and commercial satellite imagery. The OrthoEngine
Core software includes programs required to produce the input
components for orthorectified imagery including project setup,
DEM interpolation/formatting, and GCP and tie point collection.
OrthoEngine Core can also be used to create imagery mosaics.
OrthoEngine’s Airphoto Edition (for aerial photography) and
Sensor Rectification (e.g. SPOT and Landsat TM satellite imagery)
are used to perform the aerial triangulation tasks and orthorectification.
The creation of orthorectified SPOT and Landsat TM imagery
using the OrthoEngine Core and Sensor Rectification modules
will be the focus of this article. PCI Geomatics has created
four additional modules to the Core Kit to create digital elevation
models (DEMs) and specialty sensor models for orthorectifying
commercially available satellite imagery including the fleet
of IRS satellites, Radarsat, and Ikonos:
- OrthoEngine 3D Viewing and Editing - 3D Viewing, feature
extraction and editing
- OrthoEngine IKONOS Rectification – Orthorectification
of Space Imaging’s Ikonos satellite imagery at 1meter and
4 meter resolutions
- OrthoEngine Automatic DEM - Autocorrelation of optical
stereo satellite imagery to produce DEMs
- OrthoEngine Automatic RADARSAT DEM – Orthorectification
and Stereo DEM production
The OrthoEngine Sensor Rectification software currently supports
processing of ephemeris data and orthorectification for the following
commercial imaging satellites:
- Landsat 4, 5 and 7
- SPOT 1,2,3, and 4
- IRS 1-A, 1-B, 1-C, and1-D
- AVHRR (Canadian format only)
- ASTER
- JERS 1
- ERS 1&2
- RADARSAT (all beam modes)
The software also provides the ability to orthorectify imagery
from multiple sensors (e.g. Landsat and SPOT) into a single output
image. As stated above, orthorectification of Ikonos imagery
is supported as a module that can be purchased separately.
OrthoEngine includes access to PCI Geomatics’ Generic Database
Technology (GDB). This allows direct access (without translation)
to more than 80 raster and vector formats in their native format.
This prevents lengthy import/export operations, making the
processing much faster.
Project Setup
Project setup requires the user to specify project, name, input
and output projections, formats (i.e. what projection the
GCPs are being collected in), whether aerial or satellite
modeling, type of sensor, etc.) Large projects may require
setting up multiple project files so more than one person
can work on the project at one time. This then requires that
you export control points between project files if common
control points are desired. Project setup is straightforward
and well documented.
Ground Control Point Collection
OrthoEngine has a comprehensive suite of tools for collection
of ground control points (GCPs) and tie points for use in orthorectification.
Depending on the availability and format of the control points
and the method used, GCP collection is of -
ten the most time consuming part of orthorectification process.
GCPs can be input using a variety of methods including extraction
from geocoded the images and vector files, importing from text
files and captured from hardcopy sources using a digitizing
tablet. GCPs can also be collected from source data in more
than one input projection. A minimum of four GCPs is required
for each satellite image, although six to eight are recommended.
Tie Point Collection
When orthorectifying multiple scenes within a project area,
tie points are typically acquired. Tie points are produced
by identifying the same pixel location in two or more images
within their overlap areas. OrthoEngine can process tie points
for an unlimited number of input images. Unlike GCPs, tie
points do not have georeferencing information. They serve
to establish control between images, and are therefore not
required when processing a single scene. OrthoEngine has
the ability to automatically identify tie points between
two or more images. For tie points, root mean square (RMS)
residuals are calculated that identify the relative accuracy
of each point. Quality control should be performed on auto
tie points.
The bundle adjustment can be performed in OrthoEngine as an
iterative process during the GCP and/or tie point collection.
This enables the user to determine the accuracy of the block
adjustment while in process, rather than at the end. The amount
of time required to perform the bundle adjustment is dependent
on the number of GCPs collected at that time and the number
of images loaded into the project. Alternatively, to save time,
the bundle adjustment can be performed at the end of the GCP
or tie point collection.
Residual Reports
To get an overview of the control point residuals and identify
possible outliers, Ortho Engine provides the ability to generate
residual reports for all scenes within a project or for individual
scenes. Outlier points can be easily identified in the table
and edited through the use of the Edit Point function. Once
the outlier has been identified, this function will load
the images of interest, zoom to the highlighted point and
enable the GCP Collection panel for editing.
Orthorectification
The process of orthorectification typically requires correction
of terrain displacement through use of a Digital Elevation
Model (DEM). Contained within OrthoEngine is a suite of tools
providing the capabilities of importing and editing DEMs,
if necessary. The software currently supports raster formats
including USGS DEM and NIMA DTED. Tools are also provided
to generate raster data from vector/point data such as contours,
elevation points, break lines and Triangular irregular networks
(TINs). OrthoEngine also enables the input GCPs and DEMs
to be in different input projections and the output imagery
to be in a third projection. This eliminates additional processing
steps typically required at the beginning of the project.
OrthoEngine resampling options include 8 point and 16 point
sin x/x, Nearest Neighbor, Bilinear Interpolation, and Cubic
Convolution. The sin x/x resampling algorithms are uncommon
among commercial image processing software packages. Similar
to cubic convolution, they use a larger kernel size (64 pixels
for 8 point and 256 pixels for 16 point) and produce slightly
better results. However, the trade off is that these resampling
methods require more processing time. The software processing
speed can also be optimized by adjusting the computers cache
allocation. The general rule here is to select a cache size
one-half the size of your computer cache (when using Windows
NT). Modifying the sampling interval will also affect the processing
time. Large projects containing multiple scenes can easily
be batch processed to take advantage of off-hours processing.
Mosaicking Tools
Mosaicking is the process of merging two or more orthorectified
images together into a single scene. Mosaicking requires
delineation of cutlines and, in many cases, radiometric adjustment
of adjacent images to hide the seamlines and produce a more
visually pleasing product. OrthoEngine has both manual and
automatic mosaicking options. The OrthoEngine automatic mosaicking
option is ideal for projects where the following conditions
exist:
GCPs can also be imported from a PCI chip database. The Chip
Manager module (included with OrthoEngine) stores a small digital
image file identifying the location of a single GCP and information
about the sensor. It enables use of selected GCPs for multiple
projects independent of imagery type and can be queried for
criteria including area of interest, sensor type and chip resolution.
Identified points can be targeted as either GCPs or check
points. Independent check points are commonly used to evaluate
the overall accuracy of the bundle block adjustment. Stereo
points help reduce the total number of points and improve accuracy.
Stereo points are GCPs identified in the overlap areas between
two or more images. Another feature of the software is that
once a model has been established (a model requires at least
four GCPs to be collected), the software will automatically
estimate the approximate locations for new GCPs on the uncorrected
imagery. If satellite ephemeris data is used, approximate locations
can be determined with less than four points. Typically the
more GCPs collected, the better the software is at identifying
new locations. Still, the position is only approximated and
quality control and manual position of the point to its actual
location is often required.
- radiometry is fairly consistent between images,
- imagery is cloud and haze free,
- there are not significant water bodies, and
- there is not significant geometric mis-registration between
scenes.
The cut-lines generated using the automatic mosaicking feature
are non-linear, but may require editing when one or more of the
above criteria are not met. Images with significant differences
in radiometry are not always adequately balanced when using OrthoEngines
auto-mosaicking process. Manually adjusting the radiometry prior
to mosaicking is necessary in these situations. In situations
where geometric registration varies, the cut-lines may also need
to be manually defined to reduce visual offsets between scenes.
OrthoEngine has a complete suite of tools for manually mosaicking
imagery. Although more labor intensive, manual cut-lines and
radiometric adjustment give the user a lot more control in
producing a mosaic that is seamless in appearance.
Advantages include:
- Defining custom blend widths to adjust the feathering
distance between scenes,
- Color balancing of specific scenes to reduce radiometric
differences,
- Manual adjustment of brightness,
- Manual delineation of cut-lines based on clouds, terrain
variation, roads, and other factors.
Another useful tool when using OrthoEngine in the manual mode
is the ability to assess the imagery prior to mosaicking with
a mosaic preview window. The display identifies areas that may
still require editing prior to performing the mosaic process.
OrthoEngine can also mosaic orthoimages that were produced using
other orthorectification software.
Technical Support / Customer Service
PCI has a web-based Customer Service site for receiving questions
and providing answers regarding their software. Within North
America, they also offer technical service and support via
the telephone Monday through Friday from 8:00 am to 6:00
pm EST. Technical support in Europe is available for 15 hours
per day from 9:00am to midnight (Greenwich Mean Time). To
help provide more specialized support, PCI also has separate
web addresses and phone numbers to support software licensing
issues. Their new Service Liaison provides support regarding
non-technical questions such as status of a software order,
and customer feedback. Over the past several years, the authors
have received a very good customer service response from
PCI with initial response to most requests within 24 hours.
Documentation/On-line Help
Textual documentation is provided for all of the PCI OrthoEngine
modules. The manuals are well written, comprehensive and
easy to reference. They include project tutorials and step
by step instructions that walk the user through each phase
of the process. Tips are also provided for various aspects
of some processes such as GPS and tie point inexperienced
users could benefit from additional fundamental information
on photogrammetry concepts. Comprehensive on-line help is
included for each module and enables quick search and query
abilities.
Conclusions
Our experience has found that the PCI OrthoEngine Core and
Sensor Rectification modules are comprehensive, intuitive
and relatively easy to use software ideal for small to medium
sized orthorectification projects. The software can be used
for larger projects by splitting the project area into multiple
files.
Strong points include OrthoEngine’s flexibility for input formats,
and the variety of methods for GCP collection and generating
DEMs. Further flexibility is afforded by OrthoEngine’s ability
to be used in combination with other orthorectification software
packages. For example, OrthoEngine can be used to collect GCPs,
while a different software can perform the orthorectification
and/or mosaicking. Independently, OrthoEngine offers a complete
beginning to end solution for efficient production of highly
accurate orthorectified imagery products.
Reviewed by:
David Brostuen, Scott Sutton and Yusuf Siddiqui
i-cubed (information, integration and imaging, LLC)
212 Linden Street,
Fort Collins, Colorado 80524
970-482-4400
970-482-4499
dbrostuen@i3.com
www.i3.com
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