共查询到20条相似文献，搜索用时 500 毫秒
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王唤良 《中南林业科技大学学报(自然科学版)》1998,(2)
分析了高等级公路平面控制网导线边投影长度变形与测区平均高程及投影带宽度的关系．根据长度变形是否满足国家标准GB50026－93要求（≤2．5cm／1km）而确定坐标系统．给出了不同坐标系统之间的换算关系．文中算例表明：用简单算法能达到公路工程测量的精度要求． 相似文献
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在对误差的来源、误差允许值、国家统一坐标系统的有关情况进行分析的基础上,结合公路测量工作的特殊性,总结了不同地形条件下坐标系统的确定方法,从而有效解决了控制网中长度综合变形对于测量精度所造成的影响,对于实际测量工作具有一定的指导和借鉴意义。 相似文献
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《林业科学》2018,(11)
【目的】对比X射线计算机断层扫描图像重建算法中常用R-L、S-L、Cosine、Hamming和Hanning滤波器的重建图像效果,分析滤波函数重建图像质量,优选木材断层扫描图像重建中的最佳滤波器,为木材断层成像技术研究提供科学方法。【方法】依据CT成像原理,分析图像滤波过程,探讨不同滤波器工作特性和滤波器的设计步骤。首先将投影数据存放于二进制的二维数组,通过探测点编号和旋转角度确定每一点投影值,根据投影数据序列长度确定滤波器长度,将不同角度下的投影数据前后补零,使其构成3倍于原始长度的投影数据。然后进行一维快速傅里叶变换,并将频域结果与滤波器频域离散形式作乘积,对投影数据进行逐行滤波。最后,将乘积后的滤波结果进行傅里叶反变换得到时域中的投影数据,对比不同滤波器成像结果,对不同滤波器进行评价与分析。【结果】与未进行滤波的反投影重建图像相比,滤波后断层图像生长轮边界更清晰、伪影较少,边缘平滑;未经滤波处理直接反投影重建图像伪影严重,重建效果极差,生长轮、裂缝结构特征不清晰。采用R-L、S-L、Cosine滤波器滤波后断层图像边缘平滑、清晰,无向周边扩散现象,采用Hamming、Hanning滤波器滤波后图像伪影轻微,存在比较明显的波纹状伪影。从各滤波图像与检测模型图像的差异性来看,R-L滤波器滤波后图像质量最高,而Hamming滤波器滤波后结果误差最大。【结论】采用R-L滤波器得到的重建图像误差最小,图像最清晰,空间分辨率高,能有效去除伪影,滤波后的木材断层图像可准确判断缺陷形状、位置和大小。 相似文献
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提出了将三层BP神经网络算法应用于不完全投影数据的图像重建。采用新的方法确定隐含层至输出层的权值,利用误差反向传播自动调节输入层和隐含层之间的权值,使重建图像投影不断逼近原始图像投影,并采用改进的Sigmoid函数和在线调整学习速率,显著加快了网络收敛速度,提高了重建图像质量。 相似文献
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分析了不需要完全挖出根就能测定一级侧根长度,主根及其侧根的总长度,根系向土表投影的方法。这个方法是建立在研究树种根的结构规律的基础上的。 相似文献
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通过对地理信息系统中“投影变换”“镶嵌配准”“误差校正”等地图拼接方式的介绍,使地图拼接可在不同形式、不同投影参数下很精确地完成,为解决地图制图中的拼接问题提供了有力的技术手段。 相似文献
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膨胀土地基在建筑设计中非常重要。如地基发生变形,整栋楼房就要开裂、倒塌,膨胀土地基的胀缩变形是由于地基土的胀缩性及其含水量的变化引起的,因此,作者着重地论述了建筑物开裂主要原因是由:1.建筑场地土的胀缩性能及其分布的不均匀性;2.促使地基土含水量变化的外界条件;3.建筑物抵抗或适应地基不均匀变形的能力所造成的。 相似文献
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Preparation and crosslinking of oligoesterified woods based on maleic anhydride and allyl glycidyl ether 总被引：1，自引：0，他引：1
Summary Oligoesterification of wood was investigated by alternately adding esterification reactions of wood with maleic anhydride and allyl glycidyl ether. The products obtained consisted of acetone-insoluble and soluble parts. The insoluble parts were novel oligoesterified woods with oligoester chains having polymerizable double bonds. The oligoester chain length showed a tendency to decrease with increase in wood content in feed. The soluble parts were free oligoesters which were not linked with the wood matrix. The products (the oligoesterified wood-containing mixtures), when subjected to hot-pressing in the presence of a peroxide, gave plasticized crosslinked wood boards whose surfaces are smooth, glossy, and plasticlike. In this case, the free oligoesters which were hardening worked as a plasticizer for the wood components and were combined, by the crosslinking, with the oligoesterified woods, resulting in the formation of the network structure. The crosslinked wood boards exhibited outstanding properties in heat distortion temperature (>165°C) and compressive strength (ca. 1,600–2,300 kg/cm2). 相似文献
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档案内容的失真是普遍存在的,但是会计档案信息的失真就更为普遍和隐蔽,主要是由于经济活动的非公开性导致了这种隐蔽性.本文式分析会计档案信息失真的几种类型,及其产生的原因,并在此基础上探讨应采取的对策. 相似文献
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Recently, an inexpensive digital camera that can equip with a fish-eye converter lens, FC-E8, has been available from Nikon. The converter has more than 180° view angle and lens distortion. The objectives of the present study were to develop a procedure for calibrating the view angle and lens distortion of the fish-eye converter, and to examine the effect of the calibration on light environment estimates. Based on unpublished data provided by the Electric Image Technical Center of Nikon, a 12-order poly-nomial expression for the calibration was derived. The expression enabled us to calibrate the view angle and lens distortion for all selectable resolution digital images. Using a Nikon Coolpix 990 digital camera with the fish-eye converter, 105 hemispherical photographs were taken in 15 stands, and then the canopy cover and weighted openness were measured as the light environment estimates. The calibrated estimates were significantly higher than uncalibrated ones, but the differences were comparatively small, with the average differences being 0.658% for canopy cover and 0.344% for weighted openness. A strongly positive correlation between calibrated and uncalibrated estimates was observed. Both slope and intercept of the regression lines of the calibrated estimate against the uncalibrated one were significantly different between canopy cover and weighted openness, suggesting that the calibration effect would be different among light environment estimates. In conclusion, we should pay attention to the view angle and lens distortion of the fish-eye converter in estimating light environments using the Coolpix digital camera. 相似文献
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Gremmeniella abietina isolated from Pinus halepensis in Spain was characterized based on disease symptoms and conidia morphology. The disease symptoms, which became more evident in the spring, included drying up of needles and branches with some distortion of terminal twigs, resulting in dieback and sometimes to death of trees of all sizes. Variation in conidia size and growth rate was investigated between 15 isolates from Spain, and the conidia morphology was compared with four isolates from Finland, four from Switzerland and three from the US. Great variation occurred between Spanish isolates both in growth rates and in conidia size. The growth rates of the isolates were greatest on malt agar amended with pine needle extract and at 15°C. The length and the width of the conidia of the isolates from Spain ranged between 10.7–44.8 and 1.5–4.4 μm, and most of them had three septa. The results suggest that the isolates from Spain do not belong to the Alpine biotype, and the disease symptoms caused by these isolates resembled those of the European biotype. 相似文献
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