3D analysis Lecture 11 April 7 2008 3D data and Zvalue 3D data has a specified zvalue while 2D data does not Z value can be elevation rainfall temperature population Flat surface view 3D surface view Types of 3D data 3D surface Raster image and grid TIN With a regular grid of locations values stored in each grid cell Image from remote sensors Grid created by geostatistic analyst Irregular network values stored at nodes TIN created from vector data mass points breaklines polygons 3D feature shapefile geodatabase feature class 3D surface TIN surface created from vector data To create a TIN surface you start with a set of input points point features vertices of line or polygon features and connect the dots Once you have a TIN surface you can always refine it to get a better model of natural or manmade features such as lakes ridgelines graded slopes and other distinct formations You can also tag triangle faces with attribute values which allows you to symbolize a TIN not only by elevation slope or aspect but by any other characteristic you like vegetation land use and so on Rules of Delaunay triangulation methods 1 The triangles are as equi angular as possible thus reducing potential numerical precision problems created by long skinny triangles 2 A circle drawn through the three nodes of any triangle contains no other input point Some concepts in a TIN mass points are the nodes from which triangles are constructed breaklines are lines telling there is a distinct change in slope on either side of line They are used to represent surface formations like ridges streams dams shorelines and building footprints Hard breaklines capture abrupt changes in a surface soft breaklines do not affect the shape of the surface such as study area boundaries replace polygons create a flat area a single elevation value on a TIN surface They are used to model formations like building foundations terraces water body and other graded areas clip polygons Define a boundary for interpolation Input data falls outside of the clip polygon is excluded from the interpolation and analysis operations erase polygons Define a boundary for interpolation Input data falls within the erase polygon is excluded from the interpolation and analysis operations fill polygons Fill polygons assign an integer attribute value to all triangles that fall within the fill polygon The surface height is unaffected and no clipping or erasing takes place Fill polygons are used to represent continuous surface features like land cover and land use or discrete features like flood zones or endangered species habitats Breakline op Without breaklines the triangles Top Simple mass point triangulation ross the ridge of the dam does not adequately model the dam ottom With breaklines red along bothBottom The dam is successfully modele des of the ridge the TIN is retriangulated with breaklines o triangles cross a breakline replace polygons Top The blue polygon a creek will be added to the TIN as a replace polygon This is necessary because the default triangulation wrongly represents the area as sloped Bottom The replace polygon sides become triangle edges The area within Top Simple mass point triangulation does not adequately model the creek Bottom The creek is modeled with a replace polygon clip polygons Top The light blue polygon will be added to the TIN as a clip polygon Middle The TIN is clipped to the polygon extent Bottom Clipping does not actually change the extent of the triangulated area only the zone of interpolation By default triangles outside the zone are not displayed but they can be turned on as they are here erase polygons Top The light blue polygon will be added as an erase polygon Middle The polygon area is cut out of the TIN excluded from the zone of interpolation Bottom As with a clip polygon the uninterpolated area is still triangulated The erase polygon sides become triangle edges fill polygons Top The polygon layer will be added to the TIN as fill polygons Middle The TIN is retriangulated The blue lines indicating polygon boundaries become triangle edges They look wavy but they are straight line segments Bottom The TIN is symbolized by the polygon attribute values 3D feature 3D feature is used to display discrete geographic features like buildings rivers and wells on or beneath surfaces 3D features can be stored in shapefiles or geodatabase feature classes In ArcScene you can also render 2D features in 3D by manipulating their layer properties 3D feature classes can be identified by the ZM values in the Shape field of their attribute tables Create 3D features 3D features differ from 2D features in that they store a z value as part of their spatial definition 3D features can be converted from existing 2D features or can be created from defining a new feature class to be 3D when you create it Converting 2D to 3D To convert a 2D layer to 3D you need z values There are three ways to get z values From a raster or TIN layer that shares a common spatial extent with the 2D features From an attribute in the 2D layer attribute table By typing a value which is then applied to all features in the 2D layer If the 2D layer is a point layer each feature gets a z value If it is a line or polygon layer each feature vertex gets a z value Creating and digitizing 3D features create a feature layer and specify it store z values in ArcCatalog digitize the feature layer in an ArcMap edit session if your map document contains a raster or TIN layer The 3D digitizing tools one for points one for lines and one for polygons are located on the ArcMap 3D Analyst toolbar Digitized 3D features have a z value for every vertex you digitize Just like features that are converted from 2D to 3D they also have vertices at cell size intervals if you are digitizing on a raster or where features cross triangle edges if you are digitizing on a TIN Other conversions raster raster TIN to TIN to to feature vector to TIN feature 3D raster Raster to TIN When a raster is converted to a TIN a certain number of raster mesh points become nodes in the TIN A mesh point is a location where four cell corners meet The number of mesh points used to create the TIN is the smallest number that satisfies two conditions First the output TIN must cover the entire surface area of the input raster Second a user specified z tolerance must be met The z tolerance is a number that limits z value differences between the input and output surfaces A large z tolerance allows the TIN surface to