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Example 36  Modeling panoramic cameras (Fisheye, 360°/180°)

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Example 36  Modeling panoramic cameras (Fisheye, 360°/180°)

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Example 36  Modeling panoramic cameras (Fisheye, 360°/180°)

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Panoramic cameras are useful for monitoring small spaces.

The view area of such cameras is a hemisphere. Field of view is projected on the image sensor in the form of a circle.

Therefore, the original image produced by the image sensor is a circle in which the image of the scene subjected to a strong barrel distortion.

Then, in the original image a target area is cut out, distortion is corrected in this area and in result an usual frame is obtained.

Users are interested in the output frame. The original image in the form of a circle is used as an intermediate.

 

VideoCAD allows to:

Simulate the output frames without distortion with calculated pixel density;
Simulate camera field of view and distribution of the spatial resolution in the Graphics window and the 3D World.

 

See more Panoramic

 

Problem

 

There is a camera AXIS M3007-PV. The camera is mounted on a bracket at 3m height at a distance of 10 meters from a wall of 10 meters height. Camera is pointed down.

It is required to obtain a model of the control area, the distribution of the spatial resolution and image from this camera.

 

Camera parameters according to manufacturer's specification, crucial for modeling:

Number of pixels 2592x1944 (5 MP)

 

Order of work

 

1. Create a camera by clicking the New camera button. In the New camera box, in the Camera icon combobox choose an icon for the new camera with panoramic, for example indoor/panoramic .

 

A special icon is not obligatory. In the future it will be possible to change the icon in the Camera list box.

 

2. Place the camera on the layout. At a distance of 10 meters from the camera create a wall of 10 m height using the Rectangle  tool.

 

3. Open the Sensitivity and resolution box and specify number of pixels on Horizontal - 2592 and on Vertical - 1944. Close the box and save changes.

 

The most important parameter that determines the image resolution of panoramic cameras, is the number of pixels of the image sensor.

 

Since the image sensor is rectangular in shape and view area of the camera is projected into a circle, not all pixels are involved in image formation.

In VideoCAD the number of physical pixels on the sensor horizontally and vertically are required. The number of pixels involved in the formation of the image (active pixels) will be calculated by VideoCAD.

High precision of specifying the number of pixels is not required. So for a 2-megapixel camera, you can enter 1200 * 900, for 3MP -1600 * 1200, for 5MP -2500 * 2000. Standard aspect ratio should be supported.

 

Lens focal length and Image size at image processing have no affect on the image resolution of a panoramic camera.

 

4. Open the Camera geometry box and specify camera installation height of 3 meters.

 

5. Click on the button to open the Sensor and Lens box.

On the Panoramic panel mark the checkbox and specify angles of installation of the panoramic camera. To point the camera down, choose:

Pan angle = 0; (this value is not important when the camera is pointed down);

Tilt angle=90.

The lens focal length boxes in the Graphics window and the Camera Geometry box will be colored by aqua-green.

 

To limit too big size of the view area projection use the Maximum distance of drawing view area box in the Camera geometry box .

 

6. Assign to the camera a Spatial resolution pattern to visualize the spatial resolution (pixel density distribution).  For this purpose open the Spatial resolution box. Clear the Active camera checkbox, then choose the pattern "Home Office Scientific Development Branch 2009 (arbitrary resolutions)" in the Pattern list. Then click Assign to assign the chosen pattern to the active camera.

 

Pattern criterion of spatial resolution for panoramic cameras must be based on the spatial resolution (Pixel per meter (Pixel per foot), Pixel for object), but not on the field of view size. Criterion Field-of-view height, % of Field-of-view for object are not suitable to panoramic cameras, because of panoramic cameras have not a stable field of view.

 

7. Enable and adjust the spatial resolution visualization in the Graphics window.

In the popup menu of the Shadow button on the Toolbar of the Graphics window choose Within projection.

In the popup menu of the Fill projection button choose Filling

In the popup menu of the Spatial resolution button choose Discrete color.

 

As a result we will see in the Graphics windows the spatial resolution distribution of the camera AXIS M3007-PV on the height specified in the Spatial resolution pattern assigned to the camera.

 

 

Considering the projection can be said, for example, that at a distance of 28 meters from the camera at a height of (2 + 0.5) / 2 = 1.25m the yellow region ends, and hence the pixel density, according to the selected pattern, equals 39 pixels per object of 1,64m height or 39 / 1.64 = 24 pixels/meter.

 

8. Open the 3D World window. In the window we can see the distribution of spatial resolution in the form of coverage on the surrounding objects.

Using the navigation in the 3D space, we can see spatial resolution at any point on the surfaces around the camera, as well as we can detect invisible areas shaded by other objects.

 

 

9. Open the 3D Video window. By directing the camera on regions of interest on the scene, we can see with what resolution these regions will be displayed by our camera.

 

10. Place 3D model of a man on the far border of yellow region, that is, where the pixel density is 24 pixels / meter. And direct the camera on the 3D model.

Let's try to change the lens focal length and make sure that only the size of the field of view is changed. Resolution of the image will remain constant.

 

 

Pan, tilt and rotation of the camera around its own axis, made in the usual way does not affect the position of the panoramic camera. By rotation the camera in the usual way, you can view images from the panoramic camera in different directions in the 3D Video. In this case, the view area will be limited at 180 degrees from the main optical axis of the lens. Beyond this limit the image is cut

 

You can change the Lens focal length, thereby changing the field of view size, but the image resolution in the 3D Video will always be maintained equal to the calculated resolution of the  panoramic camera.

If the calculated resolution is worse, the resolution of the 3D Video will be artificially reduced. If the calculated resolution is better, then the PiP mode will be launched in the 3D Video.

The Image line in the Titles displays a virtual number of pixels for correct simulation of the resolution.

 

Distortion of a panoramic camera images in the 3D Video is not modeled.

The simulated resolution is exact only at the center of the frame. Towards the edges of the frame the actual resolution is slightly worse than simulated, but this error is negligible. The smaller the view angle, the more accuracy of simulating resolution on the edges of the frame.

For a more realistic model of the image, turn on modeling of compression and smoothing, or set the actual resolution of the lens (for accurate simulation the lens resolution you also need to specify the correct size of the image sensor).

 

See also: Panoramic