>  Docs Center  >  Using ENVI  >  Open Generic ASCII Text Files

Open Generic ASCII Text Files

Open Generic ASCII Text Files

Open Generic ASCII Text Files

Use the Generic ASCII Text File Import Options dialog to specify how to format text file(s) selected for import. The dialog appears after you select an ASCII file to load.

  1. Select the Import Type, to specify how to treat the imported data:
    • Point Only (All Features are Points): Lines with coordinate data will result in a single point feature.
    • Point, Line, and Area Features (default): Strings of two or more consecutive lines with coordinate data will result in a line or area feature. All isolated coordinate lines will result in a point feature.
    • Elevation Grid from 3D Point Data: Lines with 3D coordinate data will be used to generate a triangulated terrain, which is gridded to create a elevation grid. The grid has all the capabilities of an imported DEM, including contour generation, line of sight and viewshed analysis, and raster draping. When ASCII file import settings are complete, the Elevation Grid Creation Options dialog will appear for setting up the gridding process.
  2. Select a Coordinate Column Order/Format to specify the order of the coordinate lines in the import file.
    • Coordinates can be x followed by y (longitude then latitude), or the reverse. The default is X/Easting/Longitude Coordinate First. Elevation values, if present, are always assumed to come after the x and y values. You can also use WKT or MGRS/USNG format coordinates.
    • Use Fields to Skip at Start of Line to control what column the coordinates start in. For example, if x and y coordinates are in columns 3 and 4, set this value to 2 (skip the first two columns) to ensure coordinates are read from the correct column.
    • Select the Coordinate Format to use from the drop-down list.
  3. Select the Coordinate Line Prefix to specify whether coordinates start at the beginning of the line (None, the default) or if coordinate lines start with some other sequence of characters. For example, some formats may start coordinate lines with the sequence "XY,".
  4. Specify the Rows to Skip at Start of File before extracting the data. This is useful if there are header lines at the start of the file that you want to skip.
  5. Select a Coordinate Delimeter to specify what separates the coordinates on coordinate lines. Auto-Detect is the default and the recommended method.
  6. Select the Feature Classification from the drop-down lists to assign the feature to Area, Line, and Point features imported from the file.
  7. Enable or disable the following check boxes as needed. The default settings depend on the Import Type you selected:
    • Include attributes from lines with coordinate data option: When enabled, lines that contain text after the coordinate data will be included as attributes for the feature of that coordinate. If disabled, only the lines that do not contain coordinate data will be used as attributes.
    • Column headers in first row of file: If enabled and the Import Type is Point Only, values in the first line of the file will be used at the names of attributes for the attributes found in coordinate data lines. This is useful for CSV files.
    • Treat 3rd coordinate value as elevation: When enabled, and if a numeric value is found immediately following the x and y (or lat and lon) coordinate values, that value will be treated as an elevation. Otherwise, if Include attributes from lines with coordinate data option is enabled, the value will be included as an attribute. Leave this enabled unless you are importing point data where the 3rd column is an attribute that might contain all numeric values as well names.
    • If the file contains line data, area data, or both that is delimited by a change in a particular field or column of data (versus having non-coordinate lines separating them), specify the Break Line/Area Features on Change in Field to set which field (use a 1-based index) to check for breaking the data into separate line/area features.
  8. Click the Select Coordinate Offset/Scale to open the Select Coordinate Scale/Offset dialog. Use this dialog to set an offset and scale factor to apply to each coordinate. The offset you enter in the dialog will first be added to each coordinate, then each coordinate will be multiplied by the scale factor.

Create Elevation Grid

The Elevation Grid Creation Options dialog appears if you select Elevation Grid from 3D Point Data as the import type in the Generic ASCII Text File Import Options dialog, then clicked OK after setting ASCII text import options. Use the Elevation Grid Creation Options dialog to set how to create the elevation grid using the selected layer data, and what portion of the selected overlays to use when creating the elevation grid.

  1. Set the Grid Spacing to use. The choices are Automatically Determine Optimal Grid Spacing (the default), or Manually Specify Grid Spacing to Use. If you choose manual, enter the x-axis and y-axis in the fields provided.
  2. Use the Elevation Grid "No Data" Distance Criteria slider bar to set how far an elevation grid cell can be from a known data point elevation grid cell to be considered invalid.
  3. Enable the following check boxes as needed. By default, all check boxes are disabled:
    • Use 3D Line Features as Constraints (i.e., Breaklines): When enabled, line and area features with elevation values will be treated as constraints/breaklines. This ensures that elevation values along the line/area boundary will be consistent with the elevation that should be along the line.
    • Flatten 3D Area Features: When enabled, area/polygon features with elevation will be treated as flattened areas instead of as additional 3D data points/constraints. This allows you to create flattened areas such as lakes and terrain surfaces from building models and so forth. If only 3D area features are present, grid locations outside of the areas will be marked as invalid. Otherwise, the grid locations within areas will be flattened to the area heights, and the remainder of the grid will be generated as usual.
    • Taper 3D Area Features Using Curve Value: When there are area/polygon features with elevation, enable this option and the Flatten 3D Area Features option to set edge tapering. Values less than 1 will make the edge steepness progressively greater (flatter at the middle, then steep edges), while values larger than 1 cause the steepness to be near the area centroid and flatter towards the edges. A value of 1 provides for a linear taper.
    • Ignore Zero Elevations: When enabled, this option will ignore features with an elevation value of zero. This is useful for a dataset where features with no known elevation are marked with an elevation of zero.
    • Save Triangulated Network (TIN) as a Vector Layer: When enabled, this option will create a separate vector layer with area features for each 3D triangle as part of the triangulation and gridding process. This is called the TIN surface.
    • Heights Relative to Ground: When enabled, all elevation values from the selected vector layers will be treated as relative to the height of any loaded underlying terrain surface (like a DEM). This is useful for things such as creating building models where you just know the building height above ground and not above sea level.
    • Fill Entire Bounding Box Instead of Just Inside Convex Hull: When enabled, the generated elevation grid will contain valid values filling the entire bounding box specified for the gridding operation. Otherwise, the valid values will only fill out to the convex hull polygon of the data being gridded.
  4. Click OK to save the changes.

© 2019 Harris Geospatial Solutions, Inc. |  Legal
My Account    |    Store    |    Contact Us