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Camera Geometry

 Sensor and Lens

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Camera Geometry

 Sensor and Lens

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Camera Geometry

 Sensor and Lens

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The Sensor and Lens box can be invoked by clicking the Plus button in the Camera Geometry box.

In the box it is possible to specify any image sensor size, active area size, specify lens distortion and adjust modeling active camera as a panoramic camera.

 

Click to expand
Click to expand

 

Image sensor

 

See before: Image Sensor and Active area of image sensor

 

On the Image sensor panel you can set the size and aspect ratio of the image sensor or size of active area of the image sensor.

Size and Aspect ratio boxes duplicate the Image sensor size box on the Camera geometry window, but allow you to enter the size and aspect ratio in different boxes.

 

In the Size box you can specify the image sensor size by any of the following ways:

 

Choosing a standard format (type) from the list 1/10",1/8",1/6",1/5",1/4.5",1/4",1/3.6",1/3.2",'1/3",'1/2.7",'1/2.5",1/2.3",1/2",1/1.8",1/1.7",1/1.6",2/3",1/1.2",1",4/3",1.5";

 

This traditional way of setting the image sensor size can be unaccurate for modern cameras.

 

Entering a custom format in inches, in the form of X/Y". For example: 1/7.31";

 

If you enter a format which does not exist in the list, the box turns yellow, and the Image sensor size will be calculated by VideoCAD.

 

Entering diagonal size of the image sensor in millimeters, in the form of dX.Y. For example: d6.0.

 

See more: Specifying image sensor size through its diagonal and aspect ratio

 

Entering sensor side sizes in millimeters horizontally and vertically separated by hash, in the form of W#H.  For example: 4.8#3.6;

 

See more: Direct specifying image sensor side sizes

 

In the Format box you can specify the active area side sizes of the image sensor in millimeters horizontally and vertically separated by asterisk, in the form of W*H. For example: 4.8*3.6;

 

See more: Direct specifying active area side sizes of the image sensor

 

In the Aspect ratio box you can specify the aspect ratio of the image sensor in the form of W:H. For example: 16:9 or 4:3.

 

To save changes click Save.

To cancel changes click Cancel.

 

See also: Specifying active area size of the image sensor/

 

Image sensor's active area

 

See before: Image Sensor and Active area of image sensor

 

On the Image sensor's active area panel you can specify parameters of  active area of the image sensor.

 

In the Aspect ratio box displays the aspect ratio of the active area of the image sensor. It is identical with the Aspect ratio of the output image of the camera.

 

See more: Specifying the Aspect ratio of output image

 

In  the Crop box you can set the crop factor - the ratio of cropping active area size of the image sensor when the active area does not touch the edges of the image sensor. In other cases Crop=1.

The Crop factor can be set as a vulgar fraction (separated by slash) or a real number. For example 4:3 0.67 or 16:9 720/1080. If the crop factor is not specified, it is taken to be unity.

 

 

See more: Specifying the crop factor

 

The Calculator icon invokes the Image sensor calculator box for convenient calculation of image sensor's aspect ratio, active area aspect ratio and the crop factor.

 

The Horiz., Vert. and Diag. boxes display sizes of the active area of the Image sensor, which are used in modeling the camera.

These sizes are calculated based on the size and aspect ratio of the image sensor, as well as the aspect ratio of the output image.

 

In the boxes, you can directly type any sizes of the active area of the image sensor in millimeters.

In this case, the aspect ratio of the active area will be defined by the ratio of its sizes. The Aspect ratio box will show Custom.

By this method, you can specify an arbitrary aspect ratio of the image and camera angles. To set arbitrary camera angles choose the sizes of the active area of the image sensor.

 

Below you can see the dynamic image showing the position and relative sizes of the active area on the image sensor (aqua color) subject to the selected aspect ratios and crop factor.

 

Examples of images of image sensor of real cameras:

 

Aspect ratio of Image sensor

4:3

16:9

4:3

16:9

16:10

16:10

16:9

(1920*1080)

Aspect ratio of Active area of Image sensor

4:3

16:9

16:9

4:3

16:9

4:3

16:9

(1280*720)

Crop

1

1

1

1

1

1

720/1080=0.67

Image

 

To save changes click Save.

To cancel changes click Cancel.

 

See also: Specifying active area size of the image sensor/

 

Lens

 

On the Lens panel you can see:

 

Lens focal length - the box duplicates the similar box in the Camera geometry.

 

Calculated view angles are calculated from the sizes of active area of image sensor and the lens focal length.

 

Via changing sensor sizes when the lens focal length is fixed, you can set separately arbitrary horizontal and vertical view angles.

 

To save changes click Save.

To cancel changes click Cancel.

 

Lens distortion

 

See before: About Lens distortion.

 

 

 

As a rule, taking into account lens distortion is relevant for lenses with a focal length of less than 4mm. For long focus lenses, the distortion is usually can be neglected. In cases requiring precision, compare the real view angles (from the camera manufacturer's specifications or obtained by practical measuring) with the calculated view angles displayed in this box. If the angles differ by more than 1-2 degrees, the distortion of the camera lens may be noticeable. You can simulate distortion and evaluate its impact on your task.

 

To specify lens distortion:

 

1. Set or check the correct lens focal length;

 

2. Set or check format or real sensor sizes;

 

3. On the Lens distortion panel mark a checkbox near to a box of known value of real view angle (horizontal, vertical or diagonal) and enter known angle to the box. Clear checkboxes of unknown angles - VideoCAD will calculate them.

 

If real angles calculated by VideoCAD will differ from the real angles from camera specification, you can correct them, by marking a checkbox near to appropriate box. You can also change lens focal length a little. It is not recommended to change sensor sizes to correct real angles.

If you set real angle values too differed from calculated angles or set other inconsistency, then the boxed will colored in Red and (or) the view area will be corrupted.

 

4. Mark Simulate to model active camera taking into account lens distortion.

 

Simulation of distortion for all cameras can be turned on and off in the Options box > Miscellaneous > Lens distortion > Simulate distortion. There, in the Options box, you can change the discretization accuracy of distortion simulation.

 

Attention! Changing the lens focal length or the format / size of sensor at fixed real angles causes view area corruption and requires changing the real angles. Therefore, it is advisable to enable modeling distortion after a preliminary selection of proper lens to increase precision of modeling .

 

Under the influence of the lens distortion the view area becomes more complicated, it sometimes becomes infinite . To limit the distance of view area drawing use the Maximum distance of drawing view area.

 

In the 3D Video distortion is modeled with low resolution. You can obtain distorted image model with real resolution by 2 ways:

Check the Real frame size menu item then save image from the 3D Video to a file. The file will have full size, real resolution and distortion.
Use PiP. While distortion is modeled, the particular view of PIP has real resolution. In case of corruption on the corners of image with strong distortion - decrease the size of the particular view.

 

Changing the spatial resolution under the influence of lens distortion is considered along radial rays from the center of the frame to the edges, without distinguishing between horizontal and vertical.

 

Simulation of distortion increases the demand for computer power.

 

To save changes click OK.

To cancel changes click Cancel or close the box.

 

See also:About lens distortion Modeling lens distortion, Measuring real view angles of a camera

 

Panoramic

 

The panel is designed to control simulation of cameras with a view area in the form of a hemisphere (fisheye, panoramic, 360°/180° cameras).

To enable the simulation of the active camera as a panoramic camera,  check the Panoramic box.

 

In the Pan angle and Tilt angle combo boxes the angles of rotation of camera main optical axis in  horizontal and vertical planes are specified.

 

 

Thus, if the camera is mounted on a vertical wall, the Tilt angle should be zero, and Pan angle determines angle of the wall. If the camera is mounted on a ceiling, the Tilt angle must be set to 90 degrees, and the Pan angle does not matter. If the camera is mounted on the floor, the Tilt angle should be 90 degrees.

 

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

 

 

Image resolution of a panoramic camera is determined by the Number of pixels of sensor

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

 

You can change the Lens focal length, thereby changing the field of view size, but the image resolution in the 3D Video will be always 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 worse than simulated. 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 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).

 

In the Graphics window the horizontal projection of the view area and  the distribution of spatial resolution are visualized. The projection is constructed in accordance with the Within projection rule.

 

 

In the 3D World the camera coverage area and distribution of spatial resolution are visualized.

 

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Pattern criterion of spatial resolution for panoramic cameras must be based on spatial resolution (Pixel per meter (Pixel per foot), Pixel for object), but not on 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 don't have a stable field of view.

 

To draw a camera using the special icons or in the Graphics window, you need to choose thus icon during new camera creation or later on the Camera list panel. Selecting the icon works regardless of the state of the Panoramic checkbox .

 

To make a camera model a panoramic camera it is necessary:

 

Assign fisheye to the parameter Lens>Type to model the camera as panoramic.
Assign panoramic to the parameter Type>Fixed, PTZ,Dome, Mini to draw the camera using the special icons or in the Graphics window.

 

The lens focal length boxes in the Graphics window and the Camera Geometry box for panoramic cameras are colored by aqua-green.

In reports and in the exported dxf or dwg files for panoramic cameras instead of the lens focal length value the 'fisheye' word is displayed. .

 

See also: Modeling panoramic cameras (Fisheye, 360°/180°)