VrAirTrig
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ON-LINE REFERENCE DOCUMENTATION CARDINAL SYSTEMS, LLC 386-439-2525 |
VR AIRTRIG (vrat.exe) |
Type: Stand-alone Application
Current Release: 1.2.02
Aerial triangulation Application.
This application allows the collection of strip and tie points on a large number of images and performs a block adjustment using aerial triangulation methods. The Aerosys adjustment software is integrated directly with VrAirTrig to perform seamless adjustments. Several third party adjustment packages may also be used through an export and import mechanism.
VrAirTrig provides a layout tool that enables the technician to layout images of the complete project and to display all readings as either "to be read" or "completed". The intuitive interface allows the setting up, reading and export of aerial triangulation readings on up to 2000 images.
Points may be measured in one of three methods; Mono-comparator, Semi-automatic correlation assist, and Stereo. Each method is described in more detail in the Using VrAirTrig section.
VrAirTrig will start by opening the Main Window.
The Main Window in VrAirTrig contains the command pull down menus, a key-in area, two information areas, a progress bar and the coordinate display.
Commands names may be typed into the key-in area at almost any time.
On the top border of the Main Window is
shown the currently loaded project.
Starting an Application (Command)
Pulling down a menu and selecting an item may start commands. Commands may also be started from a key-in using the command name. Each command name is the first three letters of the first two words on the pull down. For example: The command name for Open Project is OpePro If this rule is not followed the correct key-in is listed in parenthesis in the pull down menu after the command.
Overview
Most of your time using
VrAirTrig will be spent inside the Layout tool. This tool allows you to see all
images in the current project, and view the status of collected points. Before
starting a VrAirTrig project, you will need raw images, a ground control file,
and a camera calibration report.
The following steps
would represent a typical workflow when using VrAirTrig:
1. Assemble
images, ground control files, and camera calibration information.
2. Create
a new camera file if one does not already exist for the camera calibration
report. This can done with the Camera->Create pull-down menu.
3. Create
a new coordinate file if one does not exist. This can be done with the
Coordinate->Create pull-down menu.
4. Create
a new project file using Project->Create. The project file contains a list
of all images used in the project. The project dialog is used to set image attributes
such as filename format, strip location, and pixel size.
5. Use
the Layout->Set Photo Positions to set the initial positions of the photos
for the Layout tool.
6. Open
the layout tool using the Layout->Open Layout pull-down menu.
7. Use
measure tools to measure strip and tie points.
8. Adjust
points to create final solution.
Measuring Points
When measuring points one of three methods of measurement may be used at each point. Because the ground features will change from point to point where one point may be on a city street and the next may be in trees one method of measurement will not suffice in all situations. The three methods of measurement are:
- Mono-comparator– A common point is selected in the left or upper image and the same point is selected on the right or lower image.
- Semi-automatic correlation assist – The cursor is positioned on one image and its corresponding location is found on the other image
- Stereo – Images are displayed in stereo and parallax is cleared at the point location. This operation is similar to the method used on analytical stereo-plotters. Options in this mode include image correlation, dove prism adjustment (rotation of one image) and image scale factor adjustment. There is also an option to rotate both images 90 degrees to better measure points between strips in stereo.
The three methods of point measurement are available in two environments for measuring points. Both measurement methods are used measure or re-measure pass points, tie points and ground control points. The two measurement environments are:
- Model mode – Two images are displayed in a model format. A least squares best fit is computed when at least six points have been measured. This helps avoid point identification errors. If a point has more than one ray then it is held on one image and the corresponding image must be adjusted to the held image. It is possible to start the re-measure method described below from the Model mode of measurement and return. This is useful when a point is not visible from a new strip and must be moved on all images.
- Re-measure mode – Image patches of all images that contain the point are displayed on the screen. A point may be re-measured using one of the three measurement methods.
VrAirTrig model measure mode
environment
VrAirTrig re-measure mode environment
Adjustment
The adjustment parameters dialog
There are two adjustment modes when using VrAdjust from VrAirTrig. The first is “Check Photogrammetry” in which images are formed into strips and the strips are formed into a block. This step checks the photogrammetry and yields results based on the accuracy and tie quality of the points without consideration of the ground control file. The second mode is “Full” in which the images are formed into strips and the strips are formed into a block and fit to the ground using the ground control file.
Each of the adjustment modes reports blunders. Blunders from “Check Photogrammetry” are expressed as a statistical number and blunders from “Full” are expressed in ground units. It is possible to change point weights to allow suspect points to “float” and then observe their computed position based on the block adjustment.
After an initial block adjustment it is possible to drive the layout window the blunder points. At this time it is also possible to drive to unmeasured control points and mark a control point position for re-measure and inclusion in the next block adjustment.
An example of a control point drive showing a control point on six images
The VrAirTrig Remeasure environment. Options include the ability to re-measure in mono-comparator mode, correlate mode or in stereo.
Exporting Orientation
parameters
Once the adjustment is complete, the image orientation parameters and point measurements may be exported in a variety of formats.
Point measurement formats exported VrAirTrig:
- PATB
- Albany
- JFK
- VrAt
Adjustment (Exterior Orientation) formats supported from the VrAdjust block adjustment:
- Imagestation ISAT
- Albany
- AeroSys
- PATB.