The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B4. Beijing 2008
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Figure 1
3.2 Prepare blocks
A block is a group of photos that have been organized into a
logical subset of project photos. A block can be selected for
input to the Photo Triangulation, Multiphoto Point
Measurement, and ISAT point matching and bundle adjustment.
We use the Block Preparation command(ISAT menu) to define a
block by entering an ID and then by either selecting the photos
from a list of project photos or by selecting them from a display
of photo footprints. Blocks composed of parallel flight-line
strips with side overlaps should have a one-strip overlap, that is,
they should both include a common strip. When a strip is itself
subdivided into different blocks, the blocks should have a
two-photo overlap. Spanish project includes 500 photo images
and is divided into upper and lower blocks. Block ID is A and B
with a one-strip overlap.
3.3 Perform matching
Click the ISAT Control Panel (Control Panel command, ISAT
menu) to display the ISAT Control Panel, Select block A and B,
select Auto Stretch Images, Reduce Shadow Points, Do Not Use
GPS/INS on the right side and set up other parameters, then
click submit, block A and B will be processed separately. We
can submit the process to be run immediately or schedule it for
a later time. (The Z/I Job-scheduling Service must be running
on your computer at the scheduled time). ISAT will generate tie
points between the photos, using its point-matching technique,
and perform a bundle adjustment of the points. From the
Control Panel, we can open the Job Controller or View Log File
to view information about any running, scheduled ISAT
processes or read informational messages generated by the
process. ISAT can create a block project for a processed block
in a subfolder of the current master project. The name of the
project is the ID number of the Block. ISAT regenerates pass
point IDs for each block based on its position in the list, that is,
1000001 for the first pass point in Block A, 2000001 for the
first pass point in Block B.
3.4 Edit weak areas Block A and B, review results and
adjust
After auto-matching, we can use Set Active Project(ISAT
menujor Open command(File menu) to make the Block project
as current block project, a dialog box will come out to show the
results of one or more weak areas. Use the Edit Weak Areas
command, select a weak area from a list. The area on multiple
overlapping photos, then click OK and the withheld placeholder
point as positioned on each photo will be presented in a
multi-photo point measurement environment. If there are an
adequate number of measured points in the vicinity for a good
solution, we can delete the point. Otherwise, we should
manually find and measure a nearby common reference feature
in each of the photos to connect the multi photos. Continue to
process with the same method till all weak areas are removed
from the list. Point matching automatically measures a surface
feature on multiple displayed photos when we measure it on one
of the photos. The point matching is enabled by right-clicking in
a view and then placing a check mark before Enabled on the
Matching submenu. Clear the check mark whenever you want to
disable point matching.
After edition of the weak areas, we will do compute. We can
view the tie/pass points result in the window of Photo
Triangulation Results. All the points will have the taxis with the
V(xy) value. Delete the gross error points, Blunder points and
one-ray points. Then use Multiphoto Orientation command,
select six photos from two flight-line strips, to check if there are
enough tie/pass points between photos. If necessary, input point
label in Point ID column. In the area lack of tie/pass points, we
can manually measure tie/pass points. After check, we will do
relative orientation again. View the tie/pass points result of in
the Photo Triangulation Results. If there are still big residual
error points, we can run Multiphoto Orientation command again
to adjust and re-compute. Repeat such procedure till the
accuracy is meet. The accuracy of relative orientation for this
project is RMS^i 12um.
3.5 Measure control points
This project has bundle adjustment data provided by GPS/INS,
so ground control points are less and mainly locate around
target points. Use Multiphoto Orientation command
(Orientations mean), or Point Measurement command(ISAT
menu), go into a multi-photo point measurement environment.
Input the ground control point label in the Point ID column, use
Photo\deselect and Find Photos commands to look for the
photos which will be measured and measure the ground control
points.
3.6 Merge the Block measurement results into the master
project
Select the Set Active Project or Open command(File menu),
select the master project(The Merge Block Measurements
command is available only when the master project is active).
Use Merge Block Measurements command(ISAT menu), open
Merge Block Measurements dialog box, select two blocks
separately which have been processed from Available Blocks
list, then use Merge Select Block command to merge the
generated tie/pass points with the master project.
3.7 Overall bundle adjustment; result evaluation and
adjust control points
Select Triangulation command(Orientations menu, Photo
Triangulation submenu), in Select Photos dialog box, we will
select all the photos in the master project, click OK and open
Photo Triangulation Results dialog box, click Options, select
Absolute in Adjustment Mode, select Enable Precision
Computation in Adjustment Parameters. Since this project has
GPS\INS aid for bundle adjustment, in the Given EO/GPS/INS
Settings parameters area of the Photo Triangulation Options
dialog box, select the Enable Given EO/GPS check box(If you
clear this check box, control point and tie point data alone will
be used to compute the final exterior orientation parameters).
And because this project has time parameters, we will select
