Receiving-Bay Camera Resolution Versus Storage Capacity
A regional distribution center has 64 analog cameras recording D1 resolution at 15 fps with 14-day retention. The receiving bay has two dock doors and a 12 m wide staging area; the nearest camera is mounted 18 m from the trailer seal and uses a 90-degree horizontal field of view. Three pallet shortages in eight weeks were reported, but recorded images show faces and seal numbers as unrecognizable smears. Management proposes replacing 40 cameras with 1080p IP units at 4 Mbps, 30-day retention, and a 40 TB storage array. The network team says the existing PoE switches can support the cameras but not more than 500 Mbps of aggregate recording traffic. The site operates 24/6, with a two-person overnight guard team and a remote monitoring center that receives alarms but has no live view of the yard.
1. At 18 m with a 90-degree horizontal field of view, what pixel density does a 1080p camera deliver at the target, and is it adequate for identifying a face or seal number? What would you change?
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A 1080p sensor is 1920 pixels wide. A 90-degree horizontal field of view at 18 m covers approximately 36 m of scene width, so the pixel density is 1920 divided by 36, or about 53 pixels per metre. Using commonly applied DORI-style planning thresholds, recognition requires roughly 125 px/m and identification roughly 250 px/m. At 53 px/m the camera can detect that a person is present and may show clothing colour, but it cannot reliably identify a face or read a trailer seal. A 4K camera at the same field of view would double the density to about 106 px/m-still below recognition-so resolution alone is the wrong fix.
Change the geometry. To reach 125 px/m at 18 m, the scene width must be about 15.4 m, which implies roughly a 46-degree horizontal field of view. To reach 250 px/m, the width must be about 7.7 m, or roughly a 24-degree field of view. Better still, mount a dedicated camera 5–6 m from each dock door with a narrow field of view aimed at the seal and the person handling it. Validate with a live test using a known face and a real seal number, and record the test result in the commissioning file.
2. Does the 40 TB array support 40 cameras at 4 Mbps for 30 days? Show the calculation and the practical options.
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Forty cameras at 4 Mbps produce 160 Mbps aggregate, which is below the 500 Mbps network limit. In bytes, 160 Mbps is 20 MB/s. Over 24 hours that is 20 × 86,400 seconds = 1,728,000 MB, or about 1.73 TB per day. For 30 days, 1.73 × 30 = about 51.8 TB. Therefore 40 TB is not sufficient for 30 days at 4 Mbps; it supports about 23 days before overhead. RAID and file-system overhead will reduce usable capacity further, so the real figure may be closer to 20–21 days.
Options: use H.265 or a smart codec to reduce the average bitrate to about 2 Mbps, which cuts 30-day storage to roughly 25.9 TB; reduce the camera count to 30 at 4 Mbps, which fits in about 38.9 TB but leaves little headroom; or accept a shorter retention for the 40-camera design and document the decision. Do not count on motion-based recording alone unless the policy permits gaps. Whichever option is chosen, reserve at least 10–15% capacity headroom and verify actual bitrates after commissioning rather than trusting vendor averages.
3. The remote monitoring center has no live yard view and retention is being extended. What policy and operational controls should accompany the upgrade?
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Define the purpose of monitoring before extending retention. The policy should state that cameras are for security and loss investigation, not general employee performance monitoring, and should specify who may view live and recorded video, how access is logged, and how clips are exported for investigations. Require the remote center to follow a written alarm-response matrix: which alarms trigger video verification, who calls the site guard, and what happens if no one answers. Give the remote center a live view of the receiving bay and yard only if the network and privacy review support it; otherwise provide alarm clips with a defined response time.
Retention should be risk-based: 30 days for the receiving bay and gates, shorter for low-risk areas, with legal hold procedures for incidents. Require chain-of-custody forms for exported footage, audit logs for video access, and periodic review of access rights. Post signage where required by local law, train guards on privacy and evidence handling, and test the export process before an incident. Extending retention without access control simply creates a larger privacy and evidence-integrity problem.