The Third Spatial Dimension - Introducing Geographic Information Systems with ArcGIS - page 564

In that same “From File” toolbox/tool in ArcToolbox, double-click ASCII 3D to Feature Class to
start that tool. You want to Browse for Files. Again the file you want is:
IGIS-Arc_ YourInitials \Elevation_Data\Terrain_Data\LIDAR_Points.xyz
The Input file format should, of course, be XYZ. To set the Output Feature Class navigate to
IGIS-Arc_ YourInitials \Elevation_Data\Terrain_Data\Example.gdb\Zone
and type LIDAR_multipoints in the Name field. Click Save. The Output Feature Class Type should
be MULTIPOINT. For the Average Point Spacing use either the value you wrote down above
or 16. Click OK. Wait while processing finishes. At this point you have converted the points
represented in the ASCII .xyz file to a multipoint feature class.
80. Using ArcCatalog navigate to LIDAR_multipoints (in Zone) and Preview the Geography.
It will look like a Rorschach inkblot test 11 because of the high point density (indicated by
black) and the fact that the original LIDAR file had those points which hit water masked out
(appearing white).
Zoom in on an area of the map—perhaps where a strip of white meets the black. You will see
multitudinous, irregularly spaced points. Look now at the table associated with the multipoint
file. How many records are there in the file? _________
81. Obviously, this is quite a reduction from the number of records there were when each point had
its own record. What is the maximum number of points in a multipoint? _______
82. Now it is finally time to make the Terrain feature class. It will exist inside the feature dataset
Zone, so right-click that name and select New > Terrain. Make the name My_Terrain. The
feature classes that will participate in the terrain are LIDAR_multipoints, break_lines, and
water_body, so place checks beside each. Again supply the average distance between points,
and click Next.
83. Indicate how each feature class will participate in the terrain. There are lots of choices and, if
you are building a terrain on your own you will have to do some research to determine which to
use. In this case, make this window contain the information of Figure 9-13 -- using drop-down
menus by clicking, as it turns out, the one item you need to change. Click Next. Select the
pyramid type as Z Tolerance. Click Next.
Here you come to the issue of building pyramids. Pyramids, as you may recall, is the term
used to describe files of data that are based on extensive datasets, but that are thinned
down so as to make for faster drawing. This is a convenience for some datasets. But for
the massive terrain datasets it is virtually a requirement. Further, a number of pyramid
levels can be specified for a given terrain, depending on the scale at which the terrain is
being viewed.
11 The Rorschach inkblot text was widely used, controversially, for differentiating psychotic from nonpsychotic
thinking. Make a Web search for more information if you are interested.