Estimating animal size or distance in camera trap images: Photogrammetry using the pinhole camera model
Estimating animal size or distance in camera trap images: Photogrammetry using the pinhole camera model
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DOI：
10.1111/2041-210x.13880
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发表时间：
2022-05
影响因子：
6.6
通讯作者：
Scott Leorna;T. Brinkman;Timothy J. Fullman
中科院分区：
文献类型：
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作者：
Scott Leorna;T. Brinkman;Timothy J. Fullman
随着相机陷阱已成为野生动物生态学的标准做法，开发从图像中提取附加信息的技术将提高生成数据的效用。尽管相机捕捉技术取得了快速进步，但使用捕获的图像估计动物大小或距相机距离的方法尚未标准化。直接从图像中得出动物的大小为收集野生动物指标（例如生长率或身体状况的变化）创造了机会。与动物的距离可用于量化采样设计的重要方面，例如采样的有效面积或动物在相机视野中的分布。我们提出了一种使用图像中的像素测量来估计动物大小或与相机的距离的方法，使用摄影测量中称为“针孔相机模型”的概念模型。我们使用固定的三维动物目标和在现场环境中使用活体圈养驯鹿 Rangefer tarandus 来评估这种方法的性能，这些驯鹿的大小和距相机的距离不等。我们发现，在我们的模拟中，估计动物大小或距摄像机的距离的总平均相对误差分别为 -3.0% 和 3.3%，在我们的现场设置中分别为 -8.6% 和 10.5%。在我们的模拟中，尺寸或距离估计的平均相对误差在相机模型内的图像设置之间、相机模型之间或计算中使用的测量尺寸之间没有统计差异。我们提供了在野生动物相机捕获环境中应用针孔相机模型的建议。我们使用针孔相机模型来估计动物大小或与相机的距离的方法使用单个图像产生了可靠的估计，同时保持易于实现并可推广到不同的相机陷阱模型和安装，从而增强了其在各种相机陷阱应用中的实用性，并扩大了以新颖方式使用相机陷阱图像的机会。
As camera trapping has become a standard practice in wildlife ecology, developing techniques to extract additional information from images will increase the utility of generated data. Despite rapid advancements in camera trapping practices, methods for estimating animal size or distance from the camera using captured images have not been standardized. Deriving animal sizes directly from images creates opportunities to collect wildlife metrics such as growth rates or changes in body condition. Distances to animals may be used to quantify important aspects of sampling design such as the effective area sampled or distribution of animals in the camera's field‐of‐view. We present a method of using pixel measurements in an image to estimate animal size or distance from the camera using a conceptual model in photogrammetry known as the ‘pinhole camera model’. We evaluated the performance of this approach both using stationary three‐dimensional animal targets and in a field setting using live captive reindeer Rangifer tarandus ranging in size and distance from the camera. We found total mean relative error of estimated animal sizes or distances from the cameras in our simulation was −3.0% and 3.3% and in our field setting was −8.6% and 10.5%, respectively. In our simulation, mean relative error of size or distance estimates were not statistically different between image settings within camera models, between camera models or between the measured dimension used in calculations. We provide recommendations for applying the pinhole camera model in a wildlife camera trapping context. Our approach of using the pinhole camera model to estimate animal size or distance from the camera produced robust estimates using a single image while remaining easy to implement and generalizable to different camera trap models and installations, thus enhancing its utility for a variety of camera trap applications and expanding opportunities to use camera trap images in novel ways.