The development of unmanned aerial vehicle(UAV)oblique photogrammetric technology provides a good foundation for the rapid construction of large-scale and high-definition real-scene 3D models.However,due to the limita...The development of unmanned aerial vehicle(UAV)oblique photogrammetric technology provides a good foundation for the rapid construction of large-scale and high-definition real-scene 3D models.However,due to the limitations of the modeling process,irrelevant feature data cannot be eliminated in the modeling stage.The built models contain irrelevant features and model distortions caused by errors.At present,most existing clipping algorithms cannot effectively clip real-scene 3D models that are organized as a whole or with levels of detail(LODs).Therefore,this paper proposes a novel algorithm for clipping real-scene 3D models from any perspective based on clipping boundary lines thatfit the surfaces of the models.The results of the clipping experiments for 3D models constructed with oblique UAV images show that this algorithm can effectively clip any part of the 3D models,that the clipping results of each level model closelyfit the corresponding clipping boundary lines,and that the accuracy of the clipping results is very high.Additionally,the time complexity of the algorithm is O(n^(2)).In conclusion,the algorithm proposed in this paper provides correct and effective clipping results for real-scene 3D models with LODs that are constructed with photogrammetric or 3D laser scanning data.展开更多
目的:对比三维多回波恢复梯度回波(3D MERGE)、三维可变反转角快速自旋回波(3D SPACE STIR)序列在腰椎间盘突出症(LDH)检查中的应用效果。方法:选择2020年1月~2022年11月收治的135例LDH患者,回顾性分析患者临床和磁共振成像(MRI)资料,...目的:对比三维多回波恢复梯度回波(3D MERGE)、三维可变反转角快速自旋回波(3D SPACE STIR)序列在腰椎间盘突出症(LDH)检查中的应用效果。方法:选择2020年1月~2022年11月收治的135例LDH患者,回顾性分析患者临床和磁共振成像(MRI)资料,所有患者均接受常规MRI扫描及3D MERGE、3D SPACE STIR序列扫描,对比3D MERGE、3D SPACE STIR序列测量神经根直径的一致性,评价两种序列的图像质量参数[信噪比(SNR)、对比噪声比(CNR)]、图像清晰度评分。结果:3D MERGE和3D SPACE STIR序列测量的L3~S1神经根直径比较差异无统计学意义(P>0.05),且两组序列测量的L3、L4、L5和S1直径均显示出较高相关性(r=0.957,0.986,0.975,0.972,P<0.05);3D MERGE序列的SNR及CNR均高于3D SPACE STIR序列,神经根显示分级、图像清晰度评分优于3D SPACE STIR序列,差异有统计学意义(P<0.05)。结论:3D MERGE、3D SPACE STIR序列在LDH神经根直径测量中具有极高一致性,3D MERGE序列较3D SPACE STIR序列能够更清晰显示神经跟的解剖形态,图像质量更好。展开更多
基金supported by the National Major Science and Technology Projects of China[grant no 2016ZX05050005]the Big Science Program of the International Union of Geological Sciences for Deep-time Digital Earth.
文摘The development of unmanned aerial vehicle(UAV)oblique photogrammetric technology provides a good foundation for the rapid construction of large-scale and high-definition real-scene 3D models.However,due to the limitations of the modeling process,irrelevant feature data cannot be eliminated in the modeling stage.The built models contain irrelevant features and model distortions caused by errors.At present,most existing clipping algorithms cannot effectively clip real-scene 3D models that are organized as a whole or with levels of detail(LODs).Therefore,this paper proposes a novel algorithm for clipping real-scene 3D models from any perspective based on clipping boundary lines thatfit the surfaces of the models.The results of the clipping experiments for 3D models constructed with oblique UAV images show that this algorithm can effectively clip any part of the 3D models,that the clipping results of each level model closelyfit the corresponding clipping boundary lines,and that the accuracy of the clipping results is very high.Additionally,the time complexity of the algorithm is O(n^(2)).In conclusion,the algorithm proposed in this paper provides correct and effective clipping results for real-scene 3D models with LODs that are constructed with photogrammetric or 3D laser scanning data.
文摘目的:对比三维多回波恢复梯度回波(3D MERGE)、三维可变反转角快速自旋回波(3D SPACE STIR)序列在腰椎间盘突出症(LDH)检查中的应用效果。方法:选择2020年1月~2022年11月收治的135例LDH患者,回顾性分析患者临床和磁共振成像(MRI)资料,所有患者均接受常规MRI扫描及3D MERGE、3D SPACE STIR序列扫描,对比3D MERGE、3D SPACE STIR序列测量神经根直径的一致性,评价两种序列的图像质量参数[信噪比(SNR)、对比噪声比(CNR)]、图像清晰度评分。结果:3D MERGE和3D SPACE STIR序列测量的L3~S1神经根直径比较差异无统计学意义(P>0.05),且两组序列测量的L3、L4、L5和S1直径均显示出较高相关性(r=0.957,0.986,0.975,0.972,P<0.05);3D MERGE序列的SNR及CNR均高于3D SPACE STIR序列,神经根显示分级、图像清晰度评分优于3D SPACE STIR序列,差异有统计学意义(P<0.05)。结论:3D MERGE、3D SPACE STIR序列在LDH神经根直径测量中具有极高一致性,3D MERGE序列较3D SPACE STIR序列能够更清晰显示神经跟的解剖形态,图像质量更好。