Tiepoint Measurement

By measuring image details of the same terrain object, in different images, you create tiepoints between different overlapping images.
These terrain details are also called 'Object Points' when referring to their 3 dimensional location.
Some of the tiepoints are linked to accurate terrain coordinates.
These are called the GCP's (Ground Control Points) and are introduced in the Control points dialog.
They link the project to the destination coordinate system.

The measurement of a tiepoint always happens always using the Tiepoint Measurement Window e.g.:



Each Tiepoint Measurement Window corresponds to an image in which you want to measure the tiepoint of your interest.
When you want to measure a tiepoint in different images, all necessary Tiepoint Measurement Windows are grouped together in a separate window.

Here is en example showing 3 “Tiepoint Measurement Windows” together, showing the 3 tiepoint measurements of the same object point with nr 693904:

There are two ways of getting to the group window of Tiepoint Measurement Windows.

1. Using the Orbit GIS project overview.
   This approach is especially useful in Vertical projects.
   The Orbit GIS overview gives you a clear view of where to select the tiepoints.
2. Using the menu functions.
   To open an Tiepoint Window using the menu, apply the same approach as described in 'Observations' in the chapter about the Adjustment menu.
   This approach is especially useful in Oblique projects.

In both cases you can either create new tiepoints or edit existing tiepoints.

Follow the next steps to get to the group window of Tiepoint Measurement Window's:

1. Be sure to have selected the specific Strabo mouse icon .
   It is the same mouse icon that has to be used for the opening of the Stereo Viewers.
2. Click with the right mouse button on the Orbit GIS window on the location where you want to measure a new tiepoint.
   
   
   
   
   
3. Select the 'New Tiepoint' submenu function:
   
   This will select the images under the mouse position in different colors, and popup the group window containing the Tiepoint Measurement Windows e.g.:
   
   
   
   Remark:
   
   It is important to know that tiepoints can be measured without previously having measured Fiducial Marks.
   But it is obligatory to set the correct 'scan direction' for the images before measuring tiepoints.
   It is therefore a better practice to measure the Fiducial Marks before starting measuring tiepoints in the detail images.
   The Fiducial marks nevertheless must be always available before starting stereo viewing or adjustment procedures.
4. In each 'Tiepoint Measurement Window' you have the next Navigation tools available:
   1. To measure a tiepoint follow the next steps:
      1. First zoom in to the requested detail using the functions described in points 4.2 and further e.g.:
         
         
         
         
      2. Measure the tiepoint in an image by:
         1. Press the icon.
         2. Measure the image point by clicking on the correct position with the left mouse button.
      3. A dialog will popup with a unique Tiepoint number e.g.:
         
         
         
         You are free to change that number, the software will always check if the number is unique.
         Press OK to continue.
         
         If the number introduced by you is not unique the software will prompt you with the next dialog:
         
         
         
         
      4. Execute the tiepoint measurement in all the Tiepoint Measurement Windows.
         The tiepoint number is already entered during the first measurement.
         The measurements in the other images will all get the same tiepoint number.
      5. Example after measuring the three Tiepoint Measurement Windows:
         
         
         
         
      6. Close the group window after measuring in all the Tiepoint Measurement Windows.
         
   2. The standard Pan and Zoom toolbar functions identical to the Orbit GIS windows' toolbar.
   3. The first 3 functions in the popupmenu cause the requested action to be triggered in all Tiepoint Measurement Windows at the same time:
      
      
      
      
      
      1. Pan All Photos: Panning one of the Tiepoint Measurement Windows after selecting this function, will trigger approximately the same panning in all the other Tiepoint Measurement Windows.
      2. Zoom In All Photos: Zooming in one of the Tiepoint Measurement Windows after selecting this function, will trigger the same zoom function in all the other Tiepoint Measurement Windows.
      3. Zoom Out All Photos: similar to 'Zoom In All Photos'.
   4. Select the 'Focus to Tiepoint' function to refocus at once on the tiepoint, if it already exists.
      e.g. After panning and moving the tiepoint outside the window extent.
   5. To remove the tiepoint measurement select the 'Delete Tiepoint' function.

1. Make all existing tiepoints visible by setting the 'Show Tiepoints' flag, in Strabo's View menu:
   
   
   
   
2. You possibly have to zoom in to see the image point numbers it in the Orbit GIS viewer:
   
   
   
   Example zoomed in:
   
   
   
   
3. Again: be sure to have selected the correct Strabo Mouse Pointer:
   
   
4. Click in the Orbit GIS project overview as close as possible to a cross corresponding to the tiepoint to be edited.
   Use the right mousebutton to get the popupmenu:
   
   
   
   The images that overlap the given position, will be selected and colored.
   Different tiepoints that are measured in the same image get the same color.
5. Select the 'Edit Tiepoint' submenu function to start the group window with the Tiepoint Measurement Windows:
   
   
   
   
6. Delete the existing measurement in the Tiepoint Measurement Window as follows:
   1. First zoom in on the detail:
      
      
      
      
   2. Delete the measurement in image 6939 using the popupmenu and the 'Delete Tiepoint' submenu function:
      
      
      
      
   3. After deleting the Tiepoint:
      
      
      
      
   4. Add a new tiepoint measurement:
      1. Press the icon.
      2. Add a tiepoint measurement using the left mouse button.
      3. The tiepoint cross will be drawn over the new position:
         
         
         
         
7. Close the group window.

This method uses a selectionbox with the available images, as a way to measure tiepoints in the images of your choice.
This is a recommended way of measuring tiepoints in an Oblique photogrammetric project.

Because the tiepoint measurements are inherent to Internal Orientation of the triangulation process you will find the functions under this menu:

If the project is saved all existing image points measurements are also saved in the project file.