U.S.G.S. Planetary GIS Web Server - PIGWAD

How To Create a Surface In ArcView

Requires Spatial or 3D Analyst

* indicates values we use for Mars MOLA data when converting small areas at 500 meters/pixel

Creating a GRID

A surface, or DEM (Digital Elevation Model) is usually interpolated from points, lines or polygons. 

• Add the theme that the surface is to be created from (ie. Elevation point shapefile).
• Add either of the two extensions (or add both – they do different things, but both support creation of surfaces)
  • File: Extensions
  • Activate either Spatial Analyst or 3D Analyst
    • When activated, these extensions should add multiple buttons and drop down menus, including one called Surface
• Surface: Interpolate Grid
  • Output Grid Specifications
    • Output Grid Extent: specify which shapefile to derive the grid from
    • Output Grid Cell Size:output pixel size >(*500 m/p)
      • CellSize: area, in meters, that will be interpolated to form a cell
      • Number of Rows: Automatically calculated from the cell size
      • Number of Columns: Automatically calculated from the cell size
      • Set the CellSize first, you might need to play with the cell size a few times to optimize speed with resolution – the smaller the grid size, the higher the resolution and the longer the time to calculate the grid…we could be talking hours here…(Loose Recommendation for MOLA data - CellSize is *500m for every 20² degree box of lat/long…. but don't take our word for it.)
  • Interpolation Methods
    • IDW – Inverse Distance Weighted – the farther from the center of the radius, the less weighted in the formula, depends on the radius set below
      • Z Value Field – the z component that will define the offset of the surface
      • Nearest Neighbor – IDW function is determined by the number of points
      • No. of Neighbors
      • Power – has to do with the math, do not touch
      • Barriers – if a barrier is specified, the function will not be applied past it
      • Fixed Radius – IDW function is determined by an area
      • Radius – usually a radius is calculated from the CellSize, lowering this value could significantly increase your calculation time…
    • Spline– will fit a curve over the range of the No. of Points, creating a smoothed surface (Used for MOLA)
      • Z Value Field – the z component that will define the offset of the surface
      • Weight – (*0.02)
      • No. of Points – the number of points that will define a single function (*40)
      • Type – Regularized or Tension (Tension)

Creating a TIN (3D Analyst Only)

A TIN is a triangulated irregular network.A TIN structure is comprised of points (with x, y and z values) and the triangles that are created linking the points together. All interpolation is linear.

• Surface: Creating TIN from surface
  • Active feature themes: choose the theme to create a TIN from
  • Class: refers to the type of feature in the active theme (point, line, polygon)
  • Height Source: specify the z component (x and y are taken from the dataset automatically)
  • Input as: Mass Points = each point is of equal significance in terms of its definition of the surface
  • Value Field:
  • Enter a name for the TIN, the extension is default.