Average point spacing
When a terrain dataset is created, it needs to be told the average point spacing of the input measurements. The terrain dataset uses this information to define a horizontal tiling system into which input measurements are divided. The average point spacing is used as a means to bin, or group, the points together, constructing a virtual tile system. The tile system's origin is based on the domain of the feature dataset. Specify the spacing in the horizontal units of the target feature dataset.
This system is one of the mechanisms used by the terrain to improve the performance of spatial queries. It also helps split the data up into manageable chunks. For the most part, the tile system is internal and managed by a terrain. It saves you from having to tile and chunk this data yourself.
Usually, the average point spacing is defined as part of the data procurement process and is recorded as metadata. If you don't know the average point spacing of your data, you'll need to determine what it is. The best average spacing to use for terrain is that which represents the most common distance between points and vertices. For example, there may be some points that are close, for example, 0.2 meters, and some far apart—for example, 5 meters—but if the vast majority are approximately 2 meters apart, that is the value you should specify. Outliers should have little to no influence.
When working with data from different datasets with varying resolutions, use the smallest point spacing from all the contributing datasets.
Here are some suggestions for finding the average point spacing:
- Look to metadata, the data provider, or the person responsible for maintaining the data. Point spacing is a standard piece of information used to drive the data procurement process. It should be known.
- Use the Point File Information geoprocessing tool. This tool is located in the 3D Analyst Conversion toolbox.
- Use the Measure tool on a representative sample displayed in ArcMap. Ignore large empty areas that haven't been sampled because they are over water, obscured, or outside the study area.
- The average point spacing is about estimating a tile size for the terrain dataset. You should not overload any tile with too many points; therefore, if the point spacing for the data varies significantly, use the smallest spacing involving around 200,000 points rather than the average/mean of the entire collection.
- Average point spacing should include vertices of breaklines if they represent a significant portion of the data (for example, 20% or more of total points are breakline vertices).