Building Footprints

Building footprint geometry and height attributes were extracted from 2010 ARRA LiDAR point data using ArcGIS 10 and Qcoherent’s LP360 Extractor module. All units are in feet. Feature attributes are described below. Further documentation of the data and workflow is available upon request from AMBAG. Attribute Descriptions notes – 50-character text field used for feature comments. ht_min – Minimum height derived as: [Minimum LiDAR point elevation − DEM ground elevation] ht_max – Maximum height derived as: [Maximum LiDAR point elevation − DEM ground elevation] ht_source – 10-character text field indicating which elevation source was used to record building height. DEM – DEM ground elevation for a representative point within each building feature. ndsm – Alternate building height derived from the nDSM layer, calculated similarly by sampling a representative point within each building feature. Extent – 25-character text field describing the community/region or collection of tiles within which the feature was processed. pntCnt – Number of LiDAR points classified as “Building” within the feature polygon. ELAV – Average elevation of LiDAR points classified as “Building” within the feature polygon. ELMN – Minimum elevation of LiDAR points classified as “Building” within the feature polygon. ELMX – Maximum elevation of LiDAR points classified as “Building” within the feature polygon. ELSD – Standard deviation of elevation of LiDAR points classified as “Building” within the feature polygon. ht_ave – Primary building height field. In most cases, this value is calculated as: [ELAV − DEM] In other cases, this value is derived from the nDSM field. Those cases are noted as “nDSM” in the ht_source field. Notes2 – 50-character text field used for additional feature comments, specifically identifying footprints that overlap adjacent features. Shape_Leng – ArcGIS-generated length field. Shape_Area – Feature area calculated in square feet.本数据集的建筑基底轮廓（building footprint）几何信息与高度属性，均基于2010年ARRA激光雷达（LiDAR）点云数据，通过ArcGIS 10及Qcoherent公司的LP360 Extractor模块提取得到。所有量纲单位均为英尺。 下文将对各要素属性进行详细说明。如需获取该数据集的完整文档与处理工作流程说明，可向AMBAG提出申请。 属性描述： notes：长度为50字符的文本字段，用于填写要素相关注释。 ht_min：最小高度，计算公式为「LiDAR点云最小高程 − 数字高程模型（DEM）地面高程」。 ht_max：最大高度，计算公式为「LiDAR点云最大高程 − 数字高程模型（DEM）地面高程」。 ht_source：长度为10字符的文本字段，用于标识记录建筑高度所采用的高程数据源。 DEM：每个建筑要素内代表性采样点对应的数字高程模型地面高程。 ndsm：通过nDSM图层提取的替代建筑高度值，计算方式与上述高度指标一致，即对每个建筑要素内的代表性采样点进行采样得到。 Extent：长度为25字符的文本字段，用于描述该要素所处理的社区/区域或瓦片集范围。 pntCnt：要素多边形内被分类为“建筑”的LiDAR点云总数量。 ELAV：要素多边形内被分类为“建筑”的LiDAR点云的平均高程。 ELMN：要素多边形内被分类为“建筑”的LiDAR点云的最小高程。 ELMX：要素多边形内被分类为“建筑”的LiDAR点云的最大高程。 ELSD：要素多边形内被分类为“建筑”的LiDAR点云高程的标准差。 ht_ave：主要建筑高度字段。多数情况下，其计算公式为「ELAV − DEM」；在部分场景下，该值由nDSM字段推导得到，此类场景会在ht_source字段中标记为“nDSM”。 Notes2：长度为50字符的文本字段，用于补充要素注释，尤其用于标识与相邻要素存在重叠的建筑基底轮廓。 Shape_Leng：ArcGIS生成的长度字段。 Shape_Area：以平方英尺为单位计算的要素面积。