Mount St. Helens Before and After

In this lesson you will be introduced to some of the functionality of the 3D Analyst extension for ArcView GIS.
On May 18th, 1980, the long dormant Mount St. Helens volcano erupted and over the course of several weeks the blast transformed the surrounding landscape from forested slopes into lava, ash and mud covered desolation.

What is 3D Analyst used for?

There are a wide variety of tasks that you can perform using 3D Analyst such as:

• Create surface models from different data sources (elevation, temperature.)
      
•  Determine height at any location on a surface
      
•  Find out what is visible from an observation point
      
•  Calculate the volumetric difference between two surfaces (cut and fill)
      
•  Work with 3D vector features to make realistic models of the 3D world
      
•  Visualize your data in three dimensions
      
•  Types of data used in 3D Analyst

1. Grids (raster data)

Raster data is different from vector data in that raster data is a cell-based representation of map features called a grid. The ArcView term for raster data is "Grid Data Source". A grid is comprised of cells organized into rows and columns. Each cell in the structure has a value. A group of cells with the same value represents a feature.

•  Grids represent entities
      
•  Grids are made of cells
      
•  There is a value applied to each cell

2. TINs (Triangulated irregular networks)

TINs represent surfaces using contiguous, non-overlapping triangle facets. One can estimate a surface value anywhere in the triangulation by averaging node values of nearby triangles, giving more weight and influence to those that are closer.

Where a the resolution of a grid is consistent throughout the entire grid, the resolution of TINs can vary. They are usually more detailed in areas where the surface is more complex and less detailed in areas where the surface is simpler. Because of the detail of TINs, little information is lost when doing analysis.

In general, Grids tend to be used for smaller, regional applications while TINs are used for more detailed, larger scale applications.

Don't forget to set your project's Working Directory at the beginning of this exercise!

Before you begin this lesson you will need to download the data that is used throughout the exercise. The dataset for this lesson is available in .ZIP or .EXE format. Using the .EXE file, the data will be extracted to the correct folder when you double-click the downloaded file to execute it. If you are unable to download the .EXE file due to your network or service provider's security measures, download the .ZIP file and be sure to extract the data to the folder indicated in the lesson instructions. If you cannot download either of the files available here, contact your system administrator. If you have any questions, send an e-mail to K-12@esricanada.com.

ArcView 3.x
Setup.exe or Winzip File	PDF or WordDoc