如果一张图片说千言万语，3D模型说了多少个单词？无人驾驶飞行器（UAV）图像和视频一直是许多领域的游戏更换器，如建筑检查，建设进度监测和灾害后的调查损坏。图像和视频捕获很棒，但它只是无人机的完全潜力。使用称为摄影测量的复杂算法，可以将一系列简单的图像变为高度详细，精确的自然和建筑环境的3D模型。
In short, photogrammetry uses a series of overlapping images taken from different angles to compute the location of every pixel in each photo. Each image must be highly overlapped with neighboring images to capture the same features in multiple images for comparison purposes. Similar to solving an equation, the software uses the known values of picture capture location, picture capture angle, and the difference between common objects in each overlapping picture to determine the x, y, and z location of each pixel in each image. Each one of these pixels becomes a point in the 3D model.
Photogrammetry has been relegated to specialized scientific fields outside the public eye for most of its decades-long history. Recent years have seen a renaissance for this technology in self-driving vehicles and UAVs. Many production vehicles on the road today, such as those made by Tesla, use a series of cameras and photogrammetric technology as the basis for self-driving and obstacle avoidance technologies. The same technology is employed by UAV software platforms to turn simple 2D images into 3D models.
用途
Many time-consuming tasks can be performed in a fraction of the time of traditional on-the-ground methods using a drone and 3D modeling. Here are a few examples:
- 地形调查。地点横跨地点的文档。适用于一般网站侦察，切割/填充分析和产生高程产品，如表面高度轮廓或数字高度模型（DEMS）。
- Volume calculations.Measuring the volume of material in stockpiles, or the volume of soil removed from an excavation. Faster and more cost effective than traditional methods involving truck-mounted LIDAR or physical measurement.
- 建设监测。容易生成详细的，光矩形的3D模型，可以与利益相关者共享。
准确性
Is 3D modeling with a drone accurate enough to replace conventional, on the ground methods? The answer is yes in many cases, but there are caveats.
3D模型的最终精度与源图像的像素密度相关。表达像素密度最常见的方式称为地样本距离（GSD），其测量在每个像素中捕获的地面的量。1英寸/像素的地样距离意味着图像中的每个像素覆盖一个平方英寸的面积。低GSD在3D模型中的图像中的高像素密度，3D模型中的高密度，以及3D模型中的高精度。
在理想条件下，3D模型的最终精度是水平和1-3x GSD的大约1-2x的GSD。这转化为2-4厘米（0.75-1.5英寸）水平和2-6厘米（0.75-3英寸）的预期精度。最好的结果将通过高质量的相机，相对较低的飞行高度，高度精确的位置测量，最佳飞行模式以及待测表面的视野视图来获得。
If the following conditions apply to your project, it may not be a good candidate for photogrammetric modeling:
- Heavy vegetation on the site.需要测量的表面需要在图片中可见。重型植被，树木和其他障碍物防止了底层表面的精确测量。
- 网站上的高障碍物。A drone operator must have freedom to choose the optimal flight altitude and pattern for best results. Tall equipment, power lines, towers or other obstructions may necessitate flying at a higher-than-optimal altitude or using a suboptimal flight pattern.
- 需要真正的调查级准确性。虽然3D建模在正确执行时非常准确，但它不是真正的调查。如果您需要进行法律目的或需要最高的准确性调查，最好得到完整的地面调查。
- FAA regulations.由于靠近机场和其他敏感区域，有些网站可能位于受限制的飞行区域。此外，FAA法规禁止未经保美人员的航班。无法清除人员或旁观者的网站可能不是一个不错的选择。
Generating an accurate model of a site requires careful planning, specialized equipment, and a site with suitable conditions. An experienced drone operator will be able to assess the viability of a site by checking the airspace regulations, surface conditions, and asking the right questions. Braun Intertec has the equipment, experienced personnel, software, and knowledge to measure topography, calculate volume, generate detailed 3D building models, and many other efficiency-boosting uses. Contact our UAV team to explore the possibilities for your site.