西约克郡警察的成像团队因其创新的3D激光扫描和CCTV技术而实现了一系列刑事定罪。

丹·夏普（Dan Sharp）看到西约克郡警察正在为犯罪现场测量师做广告时，他正在担任电气测量师，并引起了他的兴趣。他申请，找到了工作，再也没有回头。今天，他是韦克菲尔德（Wakefield）的高级成像官，管理着一支民用团队，该团队为四个区域约克郡部队提供法医成像服务，并应要求在全国各地其他部队提供。他们与一系列媒体合作，包括视频，摄影，CCTV和2D/3D建模。

尽管举止适当，但Dan还是使用CCTV与3D激光扫描技术开发了一些革命性的法医技术应用。3D激光扫描有时也称为LiDAR，用于生产高度准确的3D“点云”（扫描），用于3D数字建模。

弄清楚如何以这种方式解决复杂的证据挑战，赢得了丹（Dan）的国家创新奖，莱卡·吉尔斯特（Leica Geosystems）是英国警察部队的3D激光扫描设备的领先提供商。它还将他带到了拉斯维加斯的一次会议，在那里他向来自美国各地的警察提出了技术，他们说他们“从未见过类似的东西”。

Laser scanning and ‘image stitching’

3D laser scanning’s ability to create highly accurate digital models of crime scenes is impressive enough. The non-intrusive technique helps CSIs to prevent contamination of the scene, and the results can help investigating officers, lawyers and jury members to ‘walk through’ the scene at any time, even years later, and verify details such as distances and lines of sight.

更令人印象深刻的是，可以将3D扫描与现场或附近拍摄的照片或视频剧照一起“缝制”。有时，这种缝制纯粹是为了在模型中添加兴趣点/现实主义或帮助观众更好地了解他们的看法。

然而，当丹的同事带给他一系列令人头疼的现场案例，其中有闭路电视录像，但缺乏证据意义时，他被迫比以往任何时候都更进一步。

首先,他被问及快速破裂户外CCTV footage could be used to ascertain the speed of a pedestrian. Second, could CCTV footage be helped to corroborate or eliminate suspects in robbery cases? And third, based on the known locations of two bullet holes, was it possible to establish where the shooter had been standing and whether the gun had been aimed at police officers?

Initially, Dan and his colleague had no idea. But with his expert knowledge of his Leica 3D scanners and software, and his ability to ‘stitch’ digital images into his 3D scans, Dan said he’d give it a go.

A string of convictions

丹的努力得到了回报。他开发了三种涉及3D“点云”（扫描数据）模型与CCTV录像中的剧照的技术：可疑身高分析，速度分析和子弹轨迹分析。They’ve since been relied upon in court many times by many police forces: to the best of Dan’s knowledge, the evidence they produce has never been shown to be flawed, never been successfully argued by the defence, and never failed to contribute towards a conviction.

Over the past eight years, Dan’s three methods have been used by the growing Crime Surveying team at West Yorkshire Police, helping to secure convictions for serious crimes including murder, armed robbery, death by dangerous driving, arson with intent to endanger life, and the attempted murder of a police officer. And while the team doesn’t get a mention in the press when cases result in convictions, ‘crucial CCTV evidence’ is often noted!

Unsurprisingly, news of西约克郡警察’s在这一领域的工作继续蔓延，他收到了四个约克郡部队及其他地区的大量要求。第二种力量埃塞克斯（Essex）最近也开始使用速度分析技术。

决定何时应用该技术

根据Dan的说法，并非每种情况都适合这些方法。“在每种情况下，我们需要做的第一件事是查看我们在录像方面所拥有的东西 - 我们可以看到我们需要看到的东西吗？帧速率足够高吗？自事件发生以来，现场发生了根本变化吗？这个录像可以在法庭上站立吗？我们只有在认为我们有现实的机会来产生一些独立或证实证据的机会时才开始流程。

“这一过程可能会很费力 - 从几天到几周的时间里访问犯罪现场，评估镜头，将图像拼接在一起，分析发现并写出我们的报告。但这是值得的：我们能够向法院提供这么小的错误幅度，以至于我们证据错误的机会很小，有时数百万到一个。”

丹和他的团队定期陪同他们的证据向法庭。3D模型提供了重要的证据，但它们也帮助证人以更容易理解的方式做出证词（“我站在这里”，“我看不到我的位置”）。而且，由于可以旋转和放大模型，因此它们可以帮助判断和陪审员权衡该证词，并在现场的关键人物和证据方面定义。

Innovation award

The laser scanning equipment Dan used to develop his techniques is from Leica Geosystems, a global optics company with its UK headquarters in Milton Keynes. He used a Leica laser scanner with Leica Cyclone 3D point cloud processing software. Today, the team has three different types of Leica laser scanner to call upon.

Mike Skicko is the lead for forensics at Leica Geosystems in the UK and has known Dan for some years. “We’ve been really impressed by the way Dan has taken existing technologies and found clever new forensic applications for them.”

“What might once have been impossible, or at best have taken ages to piece together using 2D photos, measuring tapes and a lot of maths – with a big risk of human error and significant margins of tolerance – can now be done very quickly and accurately. It’s why West Yorkshire Police won Leica’s HDS (high definition surveying) Award for Innovation in 2014, following the first bullet trajectory analysis.”

真实情况

可疑身高分析

Until Dan tried his height analysis technique, his force had been paying an external consultant to use traditional photogrammetry to analyse suspects’ images from the scene. This was slow, delivered only 2D models, and had a 2” margin of error either way – which is large, because a lot of the population would fall in the height grouping of, say, 5’7” to 5’11” tall.

But by stitching 3D laser scans and CCTV together, and adding some basic trigonometry techniques, Dan found he could assess a suspect’s height much more accurately, slashing the margin of error to just 0.6” either way. In that example, therefore, this would narrow the pool of suspects to those measuring between 5.84” and 5.96”. This can help the police to dismiss or corroborate evidence about suspects.

在利兹的餐馆和酒吧进行了一系列五次武装抢劫，这项技术证明是无价的。三名嫌疑人在闭路电视上反复抓获，但他们的脸被遮住了，没有留下足迹或指纹。手机数据将犯罪嫌疑人置于附近，但没有足够的结论。

Dan’s technique found that the three suspects must measure 5’4”, 5’11” and 6’5” (he nicknamed them Small, Medium and Large). He found that the suspects’ heights were the same at every crime, indicating that the same men were involved in each. Using percentile height charts for the male British population, Dan found that the chances of these suspects not being the same three individuals together on the footage was millions to one. The suspects had originally refused to be measured, but when Dan’s evidence led to arrests the suspects could be measured in custody. They were found to be very close to the heights Dan had calculated.

Speed Analysis

Dan’s first use of 3D laser scanning and CCTV images to calculate speed came after the high-profile killing of a church organist in Sheffield on Christmas Eve. The suspects claimed they had simply been walking behind the man, but that when they overtook him a scuffle had ensued, and that the man had accidentally been killed. And there was limited evidence to the contrary.

However, Dan was provided with night-time CCTV footage which briefly showed first the victim and then the suspects walking along the road. He scanned the area and calculated the exact walking speed of the victim and suspects. He found that the suspects had been walking more slowly than the organist and could never have caught up without a significant change of pace. The suspects must have deliberately accelerated from 3mph to 14mph – in other words, from a slow walk to a sprint – to attack and viciously beat the organist and seize his briefcase. This proved their intent, and one suspect was sentenced to a minimum of 25 years for murder while the other received nine years for manslaughter.（英国广播公司的新闻）

The same technique can be used to determine vehicle speed. In one case, a car driver denied speeding after hitting and killing a pedestrian in Rotherham. There were no skid marks on the road and no witnesses. However, CCTV footage from the exterior of a nearby house showed a partial view of the road. It was enough for Dan’s team to prove speeding: the driver was jailed for eight years and banned from driving for 14 years.（英国广播公司的新闻）

Bullet Trajectory Analysis

在2011年的伯明翰暴动中，有41名蒙面和连帽衫的男子纵火向酒吧着火，以吸引警察到现场。开枪射击，但犯罪嫌疑人声称他们只是在空中射击。西米德兰兹警察局听说了丹的部门的工作，并问他们可以用两个子弹孔做什么：一轮在嵌入墙壁之前穿过二楼的窗户。

最初，丹不确定他们能提供帮助。但是，他与同事一起调查了现场 - 只是发现窗户已经被替换。但是，通过扫描房间并在受损窗户的CSI照片中缝制，他重新创建了窗户孔的确切位置。将其与墙壁上的孔连接起来，返回射击者唯一可能的射击位置，一个1m2的地面 - CCTV镜头确定了一个在那个确切时间站在那里的嫌疑人。

Dan then stitched the four attending police vans into the scene and mapped the entire trajectory of the bullet, proving that it had missed a police officer’s head by just three feet. A ballistics expert said that a trajectory of just 1.2° lower would have resulted in a head-shot to the police officer, and that the shooter’s 1.2° ‘error’ could be accounted for simply by the pulling of the trigger. The court accepted intent to kill.

该概念证明花了丹的团队六个星期才能弄清楚，然后在法庭上征求六个星期。这导致因未遂谋杀而定罪，除其他外，射手被判处29年徒刑。（英国广播公司的新闻）

What is 3D laser scanning/LiDAR?

LiDAR stands for light detection and ranging, and it’s carried out using a 3D laser scanner – a bit like a camera – which fires out thousands of laser pulses per second in every direction. When they hit surrounding objects, these pulses reflect back and are recorded by the scanner. The delay between sending and receiving allows the scanner to calculate spatial distances to a very high degree of accuracy.

扫描仪生成的“点云数据”是通过专业软件进行的，然后构建了现场的复杂数字3D模型。这提供了场景中所有对象之间的永久高精度测量，例如，可能包括车身，武器和门口。您甚至可以在3D模型的不同部分内“站在”，从而随时甚至在几年后重新创建犯罪现场。

激光扫描节省了大量时间，足够准确，可以在法庭上依靠，并有助于防止犯罪现场污染。例如，您可以在门口放置扫描仪，并在踏上现场之前进行所有测量。