Starting a Stereo Viewer

Follow the next steps to start a Stereo:

In the view menu, check if the wanted visualisation methods are selected.

1. Select a viewer mode:
   • Anaglyph Mode
   • Strabox Mode
   • StereoGraphics Mode
2. Select the preferred rendering method:
   • Standard Refresh.
   • Buffered Refresh

This option is only active when the 'Standard Refresh' rendering method is selected.
When you select this option, contrast enhancement will be applied continuously.
This option can be de-selected while the stereo viewer is up and running.

The definition of a photogrammetric project holds a parameter defining the type of project. (see Step 1: Project Settings)
There are two possible project types.
Both types of project need another way of efficiently selecting a stereo model.

1. Vertical type
   In this type of photogrammetric project, the used images are all vertical images.
   This is the classical way of covering an area.
2. Terrestrial type
   In this type of photogrammetric project, the images are oblique.
   Mostly all images are focused on the same object.

Run through the next steps to select a model and start a stereo viewer:

The photos in the current Strabo project are all rendered in the Orbit GIS viewport.
The Strabo selection function allows you to select those photos and do something with them.

The standard mouse pointer icon will change into the Strabo Mouse Pointer .

On the OrbitGIS viewer:

1. Point with the Strabo Mouse Pointer to the location where you want to look at stereoscopically,
2. Click using the right mouse button.
   This will select the images under the mouse position and popup the extended mouse menu:
   
3. Select either 'Show Stereo Explorer', 'Show DEM Module' or 'Show Softcopy' to start the stereo viewer.
   
   Be sure to click on a location where there is overlap between at least two images.
   If you click somewhere where no stereo is possible you will see the next dialog:
   
   

For a normal vertical project, the automatic model selection is an easy way to switch between models.
This is because of the regular grid of the images.

For a project containing oblique images or terrestrial images, it is not possible to automatically select the model using the overview in OrbitGIS.
In that case the models have to be defined to be selectable.

Before defining the stereo-models, it is best to define the strips.

In the next “Strips” menu you have two functions:

1. Edit Strips…
2. Edit Strip-overlap models

Selecting ths menu shows the next dialog:

This method adds a strip number to the column “Strips”.

This method removes the selected strip in the column “Strips”.

Once a strip is selected you can add the selected photos in the column “Photos”.

Once a strip is selected in the column “Strips”, the photos in this strip are displayed in the column “Photos in Strip”.
In this list you can select a number of photos that you want to delete from the selected strip.

This method highlightes in the column “Photos”, the photos that are not yet part of a strip. These can then eventually be added to a strip with the method 'Add Selected Photos'.

This method calculates the optimum strip-configuration starting from the given set of images available in the Strabo project.
The eventually existing strips will be replaced by this strip set.

This method saves the actual strip configuration.
This information is also kept in the Strabo Project file.

The next dialog is shown when pressing on the second menu item:

The purpose of this dialog is to define how the overlap between strip is in this project.

At the left side the existing set of strip is listed.

When selecting simultaneously 2 strips in the left column, the button “Add overlap” creates for you the combination of these strips as “Strips with overlap”.
These couple forming “Strips with overlap” are then displayed in the second column.

You can remove a strip combination from the secone column “Strips with overlap” by selecting a combination and pressing the button “Remove overlap”.

In the view menu you will find the menu function 'Stereo Model' starting a submenu:

Selecting the 'Create Models…' button in the submenu will show the next dialog:

This dialog shows at the left side the images that are defined in the project.
There are some function buttons in the middle which will be explained further.
The defined models are displayed at the right side.

To create a model: select two images at the left side that form a stereo model. It is up to you at this moment to select the correct couple. In this method there is no further check whether this couple of images forms a good stereo model. Once you have selected minimum 2 images, the button 'Create Model' will become sensitive. The model should also reflect correctly which image is the left one and which is the right one in the stereo couple.

Here is a display with two images selected and one model created:

When you select more than 2 images, the 'Create Model' function will become insensitive again. This means that it is impossible to create a model when you have selected 3 or more images. Once one model is created and when at least one model is also selected two other buttons will be made sensitive: 'Delete model' and 'Reverse Model'.

If you have created one or more wrong models at the right side, then you can select the bad models and delete them using this button.

As you only can select the images in the given order, it is possible that the model has to be reversed. With this function you can switch the images in the model, make the left image the right one, and viceversa. Compare with the previous image above to see an reversed model:

This function is only sensitive in a photogrammetric project of type 'Vertical'. Pressing this button will create really all couples and add them to the list of created models at the right side. No double models will be created. You can still add some not yet created models using the 'Create Model' button: e.g. you can add model 1507-1509 when this should be appropriate.

See the next dialog example:

Adding still another model e.g.:

This method creates automatically all models based on the given strip definition.

The other submenu functions in the Stereo Model' subdirectory are used to startup the stereo viewer of your choice.
All three methods let you select first a model, from the list of models that is created, and starts the viewer afterwards.

Press one of the following menu functions:

• Show model in Stereo viewer….
• Show model in DEM viewer…
• Show model in Softcopy viewer…

Pressing e.g. the 'Show model in Stereo vierwer….' menu button will start the following dialog:

Select a model from the list and press the 'Select' button to startup the Stereo viewer.
The same viewer will be started as mentioned above in “Selecting a model in a Vertical Project type”.

The 'Refresh' button will refill the model list, with the list of models that are created in the 'Create Model' dialog.
It is possible to create some extra models, during work, leaving you with an incomplete list in this dialog.
Closing and re-opening the dialog will also show an up to date list of models.

When you use the method 'Select a model from a list' as explained above to start a Stereo Viewer, than it is impossible to pan seamless into the neighboring models.
This means that you can capture data (using the Softcopy viewer) really to the borders of the model without switching automatically to another model.
This is sometimes an interesting possibility.
However selecting another model in the dialog, and pressing 'Select' will change the model in the viewer into the newly selected model.

This method of selecting a model is also usable in a photogrammetric project with vertical images.
However in that case, again, starting a stereo viewer from the list of models, it is impossible to pan seamless into the neighboring models.
To be able to pan seamless into the neighboring models you have to re-start the stereo viewer as described above in 'Selecting a model in a Vertical Project type' paragraph.