# The PanoramIX Authoring Tool

## Version 0.1.4.92, February 26, 1998

## 4.9 Edit Top and Edit Bottom Dialogs

Top and bottom images are optional, and any panorama may have at most one top image and one bottom image. If there is a top image, its properties may be controlled through the Edit Top dialog which is opened by selecting the entry Top in the Edit menu. Likewise, if there is a bottom image, its properties may be controlled through the Edit Bottom dialog which is opened by selecting the entry Bottom in the Edit menu. The Edit Top dialog and Edit Bottom dialogs are very similar.

The Edit Top and Edit Bottom dialogs each contain five sections:

1. Top and Bottom Image Identification
2. Top and Bottom Image Alignment Parameters
3. Top and Bottom Image Cropping Parameters
4. Other Top and Bottom Image Properties
5. Apply, Delete, and Close Buttons

### 4.9.1 Top and Bottom Image Identification

The upper part of the Edit Top and Edit Bottom dialogs provide two fields for selecting and identifying the names of the image files providing the sources of the color values and depth values for the top or bottom images. Each of these fields is accompanied by a Browse button which is intended to provide the ability to replace the indicated file with other suitable files. These functions have not yet been implemented, so these Browse buttons do nothing.

Back to the Edit Top and Edit Bottom Dialogs.

Back to the Edit Menu.

Back to the PanoramIX Authoring Tool.

### 4.9.2 Top and Bottom Image Alignment Parameters

The Edit Top and Edit Bottom dialogs provide controls for the following image alignment parameters:

a. Clipped width
b. Clipped height
c. Horizontal shift
d. Vertical shift

These parameters allow one to select a rectangular subset of each raw image to be used in creating a panoramic image. These parameters serve several purposes. The most important objective is to establish the true center of each image. That is, which row and column of the raw image corresponds to the center of the lens used to capture the image. Ideally, the true center of each image coincides with the geometric center of the raw image so that the center column index is half of the total width and the center row index is half of the total height.

The difference between the true center of each image and the geometric center of the raw data images are specified by the values of the horizontal shift and vertical shift. These values cannot be modified unless the width and height of the selected subset of the raw images have been reduced by sufficient numbers of pixels to allow the shifted image to fit within the raw image.

The initial value of the clipped width is equal to the full width of the raw top or bottom image. Consequently, the horizontal shift value cannot be adjusted until the clipped with is reduced. The clipped width may be changed in steps of two pixels corresponding to shifting the left and right edges by equal numbers of pixels symmetrically with respect to the vertical center of the clipped image.

The value of the clipped width has no effect on the panoramic images derived from the top and bottom images unless the clipped top or bottom image cannot contain the polygon defined by projecting all of the side images onto the top and bottom images, where the side images are all perpendicular to the top and bottom image planes. If the number of sides is a multiple of four, and all sides have equal widths, then the clipped width of a top or bottom image should be no less than the clipped height.

If the number of sides is not a multiple of four, or the projection of the sides does not define a regular polygon, then the clipped width of the top or bottom should be not less than ``

                wMin = sqrt(ws1*ws1 + hgt*hgt)

where "hgt" is the corresponding clipped height and "ws1" is the width of the first side image. The allows the clipped width to accommodate the circle in which the projected polygon in inscribed.

The initial value of the clipped height is determined by requiring the sum of the vertical field of view for the sides and the vertical field of view for the top or bottom to be 180 degrees. Deviations from this sum can be forced, but such deviations imply variations in camera settings or errors in camera positioning.

The vertical field of view for the sides of the panorama is determined by ``

                vfov0 = atan2(hgt0/2, radius0),

where "hgt0" is the clipped height of the first side image, and "radius0" is the radius value for the first side image. In most cases, the values of the clipped height and radius should be the same for all side images. If not, the first side image takes priority and determines the vertical field of view for the sides of the panorama.

The vertical field of view for the top or bottom image is given by ``

                vfov = atan2(hgt/2, radius),

where "hgt" is the clipped height of the top or bottom image and "radius" is the corresponding radius value. The initial value of hgt is determined by `

                hgt = 2*radius*tan(90-vfov0)

` The difference between the clipped height and the height of the raw image for the top or bottom depends on the focal length of the lens used to capture these images and the amount of overlap between the resulting images. In order to have any overlap between the side images and the top and bottom images, the focal length of the lens must be 14mm or less, for a standard 35mm film camera, assuming all sides are captured with the camera in a portrait orientation.

The values of these parameters may be modified by entering new values directly into the corresponding fields in the Edit Top dialog or Edit Bottom dialog. These values may also be altered incrementally by clicking on the associated spin controls. Changes to these values entered in either of these ways take effect when the Apply button is selected.

These values may also be controlled by selecting the edges of the corresponding areas represented in the Edit Image window. Changes to these parameters determined in this manner take effect when the mouse button is released.

Currently, there are no facilities for automatic optimization of the horizontal and vertical shift values for top and bottom images.

Back to the Edit Top and Edit Bottom Dialogs.

Back to the Edit Menu.

Back to the PanoramIX Authoring Tool.

### 4.9.3 Top and Bottom Image Cropping Parameters

As in the case of the side images, the top and bottom images need cropping boundaries to exclude peripheral garbage from the creation of blended panoramas.

The Edit Top and Edit Bottom dialogs provide controls for the following image cropping parameters:

a. Crop Left
b. Crop Right
c. Crop Top
d. Crop Bottom

As with the cropping parameters for side images, these cropping values are provided mainly to support the creation of blended panoramas, and they have no effect on panoramas created with no blending.

A visual representation of the cropping parameters is presented in the Edit Image window where the excluded areas are shown in black.

The values of all four cropping parameters must be positive integers because these serve only to exclude areas from the blending operations. In most cases, the boundaries of the excluded areas should remain outside the boundaries defined by the clipped width, clipped height, horizontal shift, and vertical shift. Such a restriction ensures that there is no gap between adjacent images. Selection of cropping boundaries which pass inside the clipping boundaries is permitted, but the blended image may acquire black areas if there is no overlap between the cropped areas of the top or bottom image and the adjacent side images.

The values of the cropping parameters may be modified by entering new values directly into the corresponding fields in the Edit Top dialog or Edit Bottom dialog. These values may also be altered incrementally by clicking on the associated spin buttons. Changes to these values entered in either of these ways take effect when the Apply button is selected.

These values may also be controlled by selecting the edges of the corresponding areas represented in the Edit Image window. Changes to these parameters determined in this manner take effect when the mouse button is released.

Initially, these values are set to zero and the cropping boundaries coincide with the edges of the Edit Image window. In this case, it can be very difficult to select these edges with the pointing device and it may be necessary to enter a small value for each cropping boundary manually to make then easier to select.

When using a pointing device (mouse) to select and drag a cropping boundary in the Edit Image window, one is not permitted to go beyond the clipping boundaries determined by the clipped width, clipped height, horizontal shift, and vertical shift. In order to force the cropping boundaries beyond this point, one must enter the cropping boundaries directly in the corresponding fields in the Edit Top or Edit Bottom dialog.

Back to the Edit Top and Edit Bottom Dialogs.

Back to the Edit Menu.

Back to the PanoramIX Authoring Tool.

### 4.9.4 Other Top and Bottom Image Properties

The Edit Top and Edit Bottom dialogs provide controls or information for the following additional image properties:

a. Field of view
b. Radius
c. Rotation angle

#### 4.9.4.1 Top and Bottom Fields of View

The Field of View field reports the horizontal field of view associated with the currently selected side image based on the clipped image width and the radius value, ``

                FovAngle = 2*atan(width/(2*radius)),

or, equivalently, `

                FovAngle = 2*atan(width/2, radius),

` Unlike the other fields in this dialog, these are read-only values which cannot be modified or specified directly. The field of view angle angle can take on values determined by the current radius and integer values of the clipped width.

In principle, the field of view of the top and bottom images, if present should be equal. In addition, the sum of the top or bottom field of view and the vertical field of view for the sides of the panorama should sum to 180 degrees. These conditions are used to establish initial clipping limits for the top and bottom images, but these initial values can be over-ridden to improve the alignment of the top and bottom images with the sides of the panorama.

The vertical field of view for the sides of the panorama is determined by ``

                vfov0 = atan2(h0/2, r0),

where h0 is the height of the first side image, and r0 is the radius value for the first side image. If the sum of vfov and the field of view for the top or bottom image differs from 180 degrees by more than a small amount, it may be necessary to consider adjusting the radius of all images so as to reduce this discrepancy.

#### 4.9.4.2 Top and Bottom Image Radius Values

The value of the radius is equivalent to that of the side images. The description of the radius value for side images should be consulted for further details.

There is a button labeled "All" next to the "radius" field. If this is selected (down), then the same radius value will be forced on all side images, as well as top and bottom images. If this button is not selected, then the radius values may be specified independently for each image. As long as the same camera and lens are used to capture all of the images with the same focusing distance and degree of image cropping, then the same value of the radius will be appropriate to all of the images comprising a single panorama.

The specified radius value(s) take effect when the Apply button is selected.

#### 4.9.4.3 Top and Bottom Image Rotation Angles

In principle, the top and bottom images are supposed to be oriented so that the center of the bottom edge of the top image and the center of the top edge of the bottom image line up with the center column of the first side image.

Standard pan-heads designed for QT-VR and similar methods provide no means of aiming a camera straight up or straight down for capture of top and bottom images. Consequently, it can be very difficult to have a camera accurately oriented when capturing top and bottom images, and the camera may easily be rotated by several degrees relative to the center of the first image.

Unlike the side images which must be corrected for camera roll angles before building a panoramic image, the top and bottom images may be rotated on-the fly for no additional cost. Consequently, there is no need for the approximate corrections based on skewing like the method used for the side images. Instead of skew values, the top and bottom image editing dialog boxes provide direct control over the image rotation angles. These angles may be entered directly in these fields, or they may be changed in one-degree steps using the associated spin controls. The specified angles become effective when the Apply button is selected.

Back to the Edit Top and Edit Bottom Dialogs.

Back to the Edit Menu.

Back to the PanoramIX Authoring Tool.

### 4.9.5 Apply, Delete, and Close Buttons

There are three buttons at the bottom of the Edit Top and Edit Bottom dialogs labeled Apply, Delete, and Close. The Apply button updates the panorama based on the currently specified properties. The Close button closes the Edit Top or Edit Bottom dialog, discarding any property changes entered since the most recent use of the Apply button. The Delete button removes the top or bottom image from the list of images comprising the current panorama, updates the panorama, and closes the Edit Top or Edit Bottom dialog.

Back to the Edit Top and Edit Bottom Dialogs.

Back to the Edit Menu.

Back to the PanoramIX Authoring Tool.

Last modified February 27, 1998.
wluken@watson.ibm.com