Find Extremum Value

Feature Description

The Find Extremum Value function is used to locate extremum points (including highest and lowest points) within specified areas on a raster dataset, identifying their positions and corresponding values. The application provides two methods to define search areas: selecting zonal data for analysis, or drawing regions directly on the raster data.

Find Extremes in Area

Feature Entry

  • Spatial Analysis Tab -> Raster Analysis group -> Surface Analysis -> Find Extremes in Area.
  • Toolbox -> Raster Analysis -> Surface Analysis -> Terrain Calculation -> Find Extremes in Area.

Parameter Description

  • Raster Data: Specify the target raster data, including its datasource and dataset.
  • Zonal Data: Select zonal data by specifying its datasource and dataset.
  • Parameter Settings: Configure extremum search parameters, including maximum and minimum extremum points to find (default: 256 for both).
  • Result Data: Statistical results will be saved as a 3D point dataset. Attribute fields store elevation values and extremum types (maximum/minimum).
  • Upon completion, the highest points in drawn regions will be highlighted in red and lowest points in blue on the current map. The output window displays extremum details including quantities and values. Note: No point information will be output when searching entire zonal data. Press Esc to clear highlights.

Search by Drawn Region

Feature Entry

  • Spatial Analysis Tab->Raster Analysis group->Surface Analysis->Find Extremes in Polygon.

Operation Guide

  • The output window prompts: "Draw a region where you want to do statistics, then right-click to perform analysis." Draw a temporary polygon as the statistical area. For drawing methods, see Draw Polygon.
  • After drawing, the "Find Extremum Value" dialog appears.
  • Set search parameters including maximum/minimum extremum points to find (default: 256 each).
  • Specify result data storage. Results will be saved as a 3D point dataset with elevation values and extremum types (Max/Min) in attribute fields.
  • Upon completion, highest points appear in red and lowest in blue on the map. The output window shows extremum quantities and values. Press Esc to clear temporary regions and highlights.
Caution:

Both zonal statistics and extremum value search perform area-based analysis, but with key differences:

  • Zonal Statistics: Analyzes raster data values within zones (vector/raster data). Generates statistical metrics (mean, standard deviation, sum, variety, range, mode, minority, median) per zone. Outputs raster and tabular datasets.
  • Find Extremum Value: Locates cell extremum points (max/min) within zonal areas of raster data. Supports selection via region objects or drawn polygons. Generates 3D point dataset with elevation values and extremum types in attributes.