概述

Hemispheric surveillance typically refers to the 180 or 360 degree views using a single lens and a single sensor. The lenses that are capable of showing the view up to 360 degrees are called fisheye lenses. These lenses have a special curved shape, allowing the light to be captured from all directions.

180 degrees or 360 degrees?
Sometimes the fisheye cameras are being referred to as 180-degree cameras and sometimes 360-degree cameras. Actually, they both refer to the same device. It simply depends on where the device is being installed. When the camera is installed onto the ceiling facing downwards, the fisheye lens can capture the 360-degree surround video. However, when being installed on the wall facing forward then only the 180-degree view in front of the camera is being covered. The 180-degree views can further be optimized by using the wedge mounts between the camera and the wall - it would tilt the camera slightly downwards, therefore showing more of the ground and less of the sky. The wedge mounts, if available, are listed under the accessory section of the product page.

What is Dewarping?
The great thing about the fisheye view is having everything covered without any blind spots. However, the fisheye view without any further processing is not very human eye friendly as the objects might appear distorted, the walls might not look straight. However, there is a great digital processing technology called "Dewarping" - it converts the circular fisheye view image into the human eye friendly panoramic image by the pixel adjustments.

Camera or VMS Dewarping?
There are two way to do dewarping - either directly inside the camera or use VMS instead. ACTi offers both solutions. The cameras with the built-in dewarping are called "Hemispheric Cameras". These cameras deliver the video stream to the VMS that has already been pre-processed inside the camera. The VMS does not need to process the image further. The benefit of using the hemispheric cameras is the easier integration with the VMS and also not consuming the computing resources on the VMS side to do dewarping there.

The cameras that do not dewarp their fisheye image are called "Fisheye Cameras". These cameras deliver the raw fisheye image to the VMS and let VMS handle the dewarping process. The benefit from the fisheye camera solution is lower cost per device compared to the hemispheric cameras.

应用

The hemispheric solutions are used when only a few cameras can be installed while almost everything has to be covered in their views. While there are less pixels per foot, the hemispheric cameras deliver very solid and seamless overview images. Good for almost any cost-driven applications, both indoors and outdoors.

解决方案

ACTi VMS supports both hemispheric and fisheye cameras. It is possible to use VMS-side dewarping on ACTi's NVR 3 or CMS 2. The adjustable grid sizes for the wide panorama views are also available in NVR 3 and CMS 2.