TOPOGRAPHIC LASER RANGING AND SCANNING Principles and Processing学习笔记

     Laser altimeter 激光高度计

     Laser profiler 激光断面仪

     Attitude 姿态

     Custom-built 定制的

     Bathymetric 海洋测深的

2.3.1 LiDARIn-Space Technology Experiment(LITE)

LITE是早期的航天激光断面(Profilers)实验，安装在STS-64航天飞机上，相比传统地球测量，这次任务更多的满足了大气、气象和气候学者的需求，主要完成了云高、气溶胶、灰尘层的测量。

11.2.2 栅格化的利弊

     Most algorithms for ground extraction employ somegeometrical reasoning to decide if a point issituated on the terrain surface. Rasterizing the data first, these algorithmscan be introduced into the domain of digital image processing,where neighborhood operations run muchfaster. However, thisresults in a loss in precision (Axelsson, 1999).

大多数滤波算法都是采用几何特征去决定某个点是否在地面上。首先栅格化，这些算法就被引入到数字图像处理的领域内，邻域搜索就能更快的进行。但是，这会造成精度的损失。

     11.2.4数学形态学滤波：

     A structureelement Δh_max(d) describing admissible height differences as afunction of the horizontal distance d is used in the erosionoperation. The smaller the distances between a ground point and its neighboring points, thelesser the height difference acceptedbetween them.相邻的两个点一般距离越近，他们之间允许存在的高差越小。(注：与图像处理中的结构元素不同，这里的结构元素是高差上限。)

     表示垂直测量精度，表示最大坡度。

The term  is the precision of the height difference of apoint pair. The set of ground points isthen defined as (Vosselman, 2000):表示同名点的高程差异测量精度，则地面点定义如下：

     The structureelement can also be determined from terrain training data consisting ofcorrectly classified ground points and vegetation points. The actualheight differences between points of the same and ofdifferent classes can be used to derive a structure element thatavoids omission errors (no real ground point is rejected as new off-terrain point) or commission errors (no real off-terrain point isclassified as ground point). By averagingthose two structure elements, the result is an optimal structure element to minimize commission and omission errors (Vosselman,2000). 结构元素可以通过已经正确分类的地面点和植被点进行获取。相同类别地物点的高差和不同类别地物点的高差都可以被用来计算结构元素，尽量避免遗漏误差和错分误差，同时这两个结构元素的平均值可以作为最优的结果。

11.2.5形态学滤波的扩展和变种

Amorphological filter variant is described by Sithole (2001), where therotationally symmetric structureelement depends on the terrain inclination estimated from averaged height data. For steeper areas, larger admissible heightdifferences are prescribed. Sithole利用从平均高程数据估计得到地面坡度信息计算具有旋转对称性的结构元素。对于越陡峭的地区，允许的高程差异越大。