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The Available Vectors List

Use the Available Vectors List to load vectors into a Vector window or to overlay them on a displayed image. You can simultaneously overlay vector layers of different projection types or overlay vector layers that have projection types different than the image. The image or the first vector layer displayed sets the projection type and all other layers are automatically converted to that projection type.

When you load a vector file into memory for the first time during an ENVI session, ENVI automatically places the vector layers into the Available Vectors List. Data files that can appear in the Available Vectors List include ENVI Vector Files, DLG, Microstation DGN, MapInfo, SDTS, DXF, ARC/INFO Interchange, and ArcView Shapefiles. If multiple vector files are opened, all of the layers for all of the files appear in the Available Vectors List sequentially.

From the Available Vectors List, select vector files to display as an overlay on an image or in a separate Vector window.

To stretch and resize the Available Vectors List, left-click on any corner of the dialog and drag to the desired size and/or shape.

Figure 3-10: Available Vectors List

Figure 3-10: Available Vectors List

Loading Vectors for Display

Follow these steps to display vector files in ENVI:

  1. From the ENVI main menu, select Window  Available Vectors List. All open vector layers appear in the Available Vectors List.

    2.  

  2. Click on the layer name.
    • To select all of the layers, click on Select All Layers.

      •  

    • To clear all of the layers, click on Deselect All Layers.

      •  

    • To remove a layer from the list, click on the name and click Remove Selected.

     

  3. Click on Load Selected in the Available Vectors List to load the vectors to a vector or display window.

    4.  

  4. When the Load Vector Layers dialog appears, select a vector destination display window by clicking on a window name.
    • If any image display windows are open, the display names (i.e. Display #1) appear in the list. Click on the desired display window name to plot the vectors over the displayed image.

      •  

    • If any vector windows are open, the vector window names (i.e., Vector Window #1) appear in the list. Click on the desired Vector window name to plot the vectors in that window.

      •  

    • To plot the vectors in a new Vector window, select New Vector Window.

     

  5. Click OK.

The Vector window appears with the selected vectors displayed (see Vector Options).

Options in the Available Vectors List

Use the Options menu in the Available Vectors List to start a new Vector window, remove all the vector layers from memory, edit the layer names, change projection types, convert layers from one projection type to another, create various world boundaries vectors, and create new empty vector layers.

Opening New Vector Windows

To start a new empty Vector window and an associated parameters dialog, select Options  Start New Vector Window.

Deleting Layers from Memory

To delete all the vector layers from memory, select Options  Remove All Layers.


Note
When vectors are deleted from memory, the only way to recover the layers is to read them from disk again.

Editing Layer Names

  1. Select Options  Edit Layer Names.

    2.  

  2. When the Edit Layer Names dialog appears, click on the name of the layer that you want to change. The name appears in the Edit Selected Item text box.

    3.  

  3. Edit the name in the text box. To return the layer to its unedited name, click Reset.

    4.  

  4. Click OK.

Changing Projection Types

  1. Select Options  Edit Layer Projection.

    2.  

  2. When the Edit Layer Projection dialog appears, select a new projection type by clicking on it (see Selecting Map Projection Types).

    3.  

  3. Click OK.

    4.  


    Note
    Changing the projection type does not affect any data points; it only changes the projection name.

To convert between projections, see the following section. For more map projection information, see Map Tools.

Converting Layer Projections

Use Convert Layer Projection to convert layers from one projection type to another.

  1. Click on the layer name in the Available Vectors List.

    2.  

  2. Select Options  Convert Layer Projection.

    3.  

  3. When the Convert Layer Projection dialog appears, select a projection type from the list (see Selecting Map Projection Types).

    4.  

  4. Enter a new layer name, if desired.

    5.  

  5. Select output to File or Memory.

    6.  

  6. Click OK.

For more information on converting projections, see Converting Map Projections.

Creating Buffer Zone Images for Vectors

Use Calculate Buffer Zone to calculate a buffer zone image in which the value of every pixel is defined as the distance from that pixel to the selected vector layers, in units of pixels. If your vectors are overlaid on a display window, the displayed image is used to create the output buffer zone image. If the vectors display in a Vector window, you must select an associated file to use for the calculation. You designate a maximum distance value and the result is that any pixels with a distance larger than that value are set to the maximum distance value +1.

  1. In the Available Vectors List, click on the names of the vectors to use in the buffer zone image.

    2.  


    Note
    If you select more than one layer, the distance is from the pixel to any of the selected layers.

     

  2. Select Options  Calculate Buffer Zone.

    3.  

  3. When the Select Associated Data File dialog appears, select the file associated with your vectors. The Buffer Zone Image Parameters dialog appears.

    4.  

  4. Click the Maximum Distance arrow increment buttons to set the maximum distance to measure, or type the value (in pixels) into the corresponding text box. Any pixels with a distance larger than this value are set to the maximum distance value +1.

    5.  

  5. From the Distance Kernel drop-down button, select Floating Point or Integer output.

    6.  

  6. Select output to File or Memory.

    7.  

  7. Click OK.

Creating World Boundary Layers

From the Available Bands List, use Create World Boundaries to create layers of various world boundaries (including political boundaries, coastlines, rivers, and USA states) from either a high resolution or a low resolution database.

  1. Select Options  Create World Boundaries. The Create Boundaries dialog appears.

    2.  


    Note
    You can also create world boundaries by selecting Vector  Create World Boundaries from the ENVI main menu.

     

  2. Select the layers by clicking the check box next to their names.
    • To select a range of layers, enter the starting and ending numbers and click Add Range.

      •  

    • To select all the layers, click Select All.

      •  

    • To clear all the layers, click Clear.

     

  3. Select one of the following options:
    • To create world boundary layers for a specific area, enter the latitude and longitude coordinates in the corresponding text boxes.

      •  

    • To create world boundary layers for the entire world, do not enter latitude and longitude coordinates.

     

  4. Select output to File or Memory. One output .evf file is created for every selected layer and named with a layer abbreviation appended to the root filename. The high resolution layers are named with a _hp, _hc, or _hr for the political boundaries, the coastlines, or the rivers, respectively. The low resolution layers are named similarly but with an _lp, etc. The USA States layer have _usa appended to the root name.

    5.  


    Note
    Building layers from the high resolution database creates very large output files (~20 MB each).

     

  5. Click OK to build the vector layers.

The selected layers appear in the Available Vectors List.

Creating New Layers

Use Create New Vector Layer to create a new empty vector layer so you can enter your own vector layers of polygons, lines, or points and attributes. These vector layers can have the same projection and geographic boundaries (size) as existing vector layers, georeferenced raster images, or can be based on user-defined input. An empty vector layer can also be created from non-georeferenced raster images for drawing vectors over those images.


Tip
You can also create vector layers by selecting Vector  Create New Vector Layer from the ENVI main menu (see Creating Vector Layers).

From Existing Layers
  1. Select Options  Create New Vector Layer  Using Existing Vector Layer.

    2.  

  2. When the New Vector Layer Parameters dialog appears, click on the name of the vector layer to use to set the projection and size boundaries.

    3.  

  3. When the New Vector Layer Parameters dialog appears, enter a layer name, and select File or Memory output.
From Projection and Boundaries of a Raster Image
  1. Select Options  Create New Vector Layer  Using Raster Image File.

    2.  

  2. When the Select Image File for New Vector Layer dialog appears, select the image file and click OK.

    3.  

  3. When the New Vector Layer Parameters dialog appears, enter a layer name, and select File or Memory output.
From User-Defined Parameters
  1. Select Options  Create New Vector Layer  Using User Defined Parameters.

    2.  

  2. When the New Vector Layer Parameters dialog appears, select the desired projection type and enter a Zone number if needed (see Selecting Map Projection Types).

    3.  

  3. Enter the bounding box coordinates in the selected projection units in the X/Ymin and X/Ymax text boxes.

    4.  

  4. Enter a layer name and select File or Memory output.

The new layer is listed in the Available Vectors List. From the Available Vectors List, you can load the layer into a Vector window and draw vectors and add attributes to it (Working with Vector Layers).

Managing Vector Files from the Available Vectors List

Use the File pull-down menu in the Available Vectors List to open new vector files, export vector layers to a region of interest (ROI) or ArcView file, and to save layers from memory to a file.


Tip
ENVI vector files can be converted to DXF using Vector  Convert EVF to DXF (see Converting EVFs to DXF Files).

Opening Files

  1. In the Available Vectors List, select File  Open Vector File  vector file type.

    2.  

  2. When the standard file selection dialog appears, select the file (see Opening Vector Files for details).

Exporting Vector Layers to a Region of Interest (ROI)

When exporting vector layers to Regions of Interest (ROIs), you can choose to create one ROI containing all of the vectors, or create one ROI for each vector.

You can also for assign unique names to ROIs when the ROIs are converted from ENVI vector files (EVFs). When you export multiple records from an EVF to separate ROIs, the output ROI name includes the vector layer name and the EVF record number, giving each ROI a unique name. Additionally, if there are attributes associated with the input EVF, you have the option of using an attribute name and value rather than the record number, as identifiers in the ROI output name.

The enhanced naming convention for the ROIs is as follows:

To export vector layers to ROIs:

  1. Choose one of the following options:
    • In the Available Vectors List, select File  Export Layers to ROI.

      •  

    • In the Vector Parameters window, select File  Export Active Layer to ROIs.

     

  2. The Select Data File to Associate with new ROIs dialog appears. Select your file and click OK.

    3.  

  3. The Export EVF Layers to ROI dialog appears. Select the Convert all records of an EVF layer to an ROI or Convert each record of an EVF layer to a new ROI conversion method. If your vector layer has attributes associated with it, a drop-down menu appears in the dialog.

    4.  

  4.  

    Figure 3-11: Dialog for Exporting EVF to ROI with Attributes

    Figure 3-11: Dialog for Exporting EVF to ROI with Attributes
    Click on the Attribute column to use for name drop-down menu to see the selection of column names. Make a selection from the list, if you wish, and click OK.

     

  5. Open the ROI Tool by selecting Tools  Region of Interest  ROI Tool from the Image window menu bar. The ROI Tool now lists the new ROIs.

    6.  

    For example, an EVF layer called vegetation exported to individual ROIs with the column attribute Veg_Type is shown in the following figure.

     

    Vector layers exported as ROIs can create very large ROIs.

 

Figure 3-12: New ROI Names After EVF Export

Figure 3-12: New ROI Names After EVF Export

Exporting Vector Layers to a Shapefile

Use this procedure to export vector layers to an ArcView-compatible fileset, which includes a Shapefile (.shp), an index file (.shx), and a database file (.dbf).

  1. In the Available Vectors List, select the vectors to export by clicking on their names.
    • To export all of the layers, click Select All Layers.

      •  

    • To select multiple layers, but not all layers, click on each layer that you want to export while holding down the Ctrl key on your keyboard.

     

  2. Select File  Export Layers to Shapefile.

    3.  


    Note
    If you decide to not load any vectors from the Available Vectors List, select File  Cancel to exit it without removing the loaded vectors from memory.

     

  3. When the Output Layer to the Shapefile dialog appears, enter the desired output filename and click OK. This dialog appears for each layer selected.

Each ArcView vector file can contain only one type of vector (polygon, point, etc.), so ENVI uses a base name and appends extensions to the base name for each vector type. The extensions used are .pg for the polygons, .pl for the polylines, and .pt for the points.

Saving Vector Layers

Vector layers listed in the Available Vectors List are currently in memory. Use this procedure to save them to a file.

  1. In the Available Vectors List, select the layer by clicking on the name.

    2.  

  2. Select File  Save Memory Layers to File.

    3.  

  3. Enter an output filename.

  ENVI Online Help (August 12, 2005)