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。
Dan Sharp was working as an electrical surveyor when he saw that West Yorkshire Police were advertising for a crime scene surveyor, and his interest was piqued. He applied, got the job, and has never looked back. Today he’s senior imaging officer in Wakefield, managing a civilian team which provides forensic imaging services for the four regional Yorkshire forces and, on request, other forces around the country. They work with a range of media including video, photography, CCTV and 2D/3D modelling.
Despite his modest demeanour, Dan has developed some revolutionary forensic technology applications using CCTV in combination with 3D laser scanning technology. 3D laser scanning is also sometimes known as LiDAR and is used to produce highly accurate 3D ‘point clouds’ (scans) for 3D digital modelling.
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”。
激光扫描和“图像缝制”
3D激光扫描能够创建高度准确的犯罪场景数字模型的能力，这是足够的。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.
Even more impressively, 3D scans can be ‘stitched’ together with photos or video stills taken at or near the scene. Sometimes this stitching is done purely to add points of interest/realism to the model or to help the viewer better understand what they’re looking at.
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，他被问及是否可以快速使用室外CCTV镜头来确定行人的速度。其次，是否可以帮助CCTV录像来证实或消除抢劫案件中的嫌疑人？第三，根据两个子弹孔的已知位置，是否有可能确定射手的立场以及枪支是否针对警察？
最初，丹和他的同事不知道。但是，借助他对莱卡3D扫描仪和软件的专业知识，以及他将数字图像“缝制”数字图像的能力，丹说他会尝试一下。
一系列信念
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西约克郡警察局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。
Deciding when to apply the technique
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。”
Dan and his team have regularly accompanied their evidence to court. The 3D models deliver vital evidence, but they also help witnesses to give their testimony in a way which is easier for the court to understand (“I was standing here,” “I couldn’t see that from where I was”). And because it’s possible to rotate and zoom in and out of the models, they help judge and jurors to weigh up that testimony and to orient key individuals and pieces of evidence within the scene.
创新奖
DAN用于开发技术的激光扫描设备来自Leica Geosystems，这是一家全球光学公司，其英国总部位于Milton Keynes。他使用了Leica激光扫描仪与Leica Cyclone 3D点云处理软件。如今，该团队有三种不同类型的Leica Laser扫描仪需要呼吁。
Mike Skicko是英国Leica Geosystems取证的领导者，并且已经认识DAN已有多年了。“ Dan采用现有技术并为他们找到了巧妙的新法医应用程序的方式给我们留下了深刻的印象。”
“曾经是不可能的，或者充其量只花了很长时间，测量磁带和大量数学 - 具有人为错误的很大风险和大量容忍度的风险 - 现在可以非常快速，准确地完成。这就是为什么在第一次子弹轨迹分析之后，西约克郡警察在2014年获得了莱卡（Leica）的HDS（高清测量）奖。”
Real cases
Suspect Height Analysis
在丹尝试了他的高度分析技术之前，他的部队一直在支付外部顾问来使用传统的摄影测量法来分析现场嫌疑人的图像。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.
但是，通过将3D激光扫描和CCTV缝合在一起，并添加一些基本的三角学技术，Dan发现他可以更准确地评估犯罪嫌疑人的高度，以任何方式将错误余量削减到0.6英寸。因此，在那个示例中，这将使嫌疑人的库缩小到5.84英寸至5.96英寸之间的嫌疑人。这可以帮助警察驳回或证实有关嫌疑犯的证据。
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的技术发现，这三名嫌疑人必须测量5'4“，5’11”和6’5”（他将其昵称为小，中和大）。他发现，嫌疑人的身高在每个犯罪中都是相同的，表明每个人都参与其中。丹使用百分位数的高度图表，发现这些嫌疑人在镜头上没有同一三个人的机会是数百万美元。犯罪嫌疑人最初拒绝衡量，但是当丹的证据导致逮捕时，犯罪嫌疑人可以被拘留。发现他们非常接近Dan计算的高度。
速度分析
Dan首次使用3D激光扫描和CCTV图像来计算速度，这是在圣诞节前夕在谢菲尔德高调杀死教堂风琴家之后。犯罪嫌疑人声称他们只是在那个男人身后走，但是当他们超越他时，随后发生了混战，该男子不小心被杀。相反的证据有限。
但是，丹获得了夜间闭路电视录像，该录像片段首先显示了受害者，然后犯罪嫌疑人沿着道路行走。他扫描了该地区，并计算了受害者和嫌疑人的确切步行速度。他发现，嫌疑人的行走比风琴师更慢，并且在没有显着速度的情况下永远无法赶上。犯罪嫌疑人必须故意从3mph到14英里 /小时（换句话说，从缓慢的步行到冲刺），以攻击并遭受恶性击败风琴师并抓住他的公文包。这证明了他们的意图，一名嫌疑人因谋杀罪至少被判处25年徒刑，而另一名嫌疑人因杀人杀而被判处九年。(BBC News)
可以使用相同的技术来确定车速。在一个案例中，一名汽车司机在罗瑟勒姆（Rotherham）击中并杀死了一名行人后否认超速行驶。路上没有打滑的痕迹，也没有证人。但是，附近房屋外部的闭路电视录像显示了部分道路。丹的团队足以证明超速行动：驾驶员被判入狱八年，并被禁止开车14年。(BBC News)
Bullet Trajectory Analysis
In the 2011 Birmingham riots, 41 masked and hooded men set fire to a pub in order to lure police to the scene. Shots were fired, but the suspects claimed they had only been shooting into the air. West Midlands Police had heard about Dan’s department’s work, and asked what they could do with two bullet holes: a round had passed through a second-floor window before embedding in a wall.
Initially, Dan wasn’t sure they’d be able to help. However, he went to survey the scene with a colleague – only to discover that the window had already been replaced. But by scanning the room and stitching in a CSI photo of the damaged window, he recreated the exact position of the window’s hole. Connecting it with the hole in the wall led back to the shooter’s only possible firing position, a 1m2 patch of ground – and CCTV footage identified a single suspect who had been standing there at that exact time.
然后，丹将四名参加警察货车缝合到现场，并绘制了子弹的整个轨迹，证明了它仅三英尺遗失了警察的头。一位弹道专家说，较低1.2°的轨迹将导致警察的头像，并且射手的1.2°“错误”可以简单地通过拉动扳机来解释。法院接受杀人意图。
This proof of concept took Dan’s team six weeks to figure out, and then six weeks to present in court. It resulted in a conviction for attempted murder, among other things, and the shooter was sentenced to 29 years in prison.(BBC News)
什么是3D激光扫描/LIDAR？
LIDAR代表光检测和射程，它是使用3D激光扫描仪（有点像相机）进行的，该扫描仪会在各个方向上发射成千上万的激光脉冲。当它们击中周围的物体时，这些脉冲会反射回并由扫描仪记录。发送和接收之间的延迟使扫描仪可以将空间距离计算至非常高的精度。
The ‘point cloud data’ generated by the scanner is put through specialist software which then builds a sophisticated digital 3D model of the scene. This offers permanent, high-precision measurements between all of the objects in the scene – which might include a body, a weapon and a doorway, for example. You can even ‘stand’ inside different parts of the 3D model, thus recreating the crime scene at any time, even years later.
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。
