ENVI Vector Windows

ENVI provides a stand-alone GIS plot window for displaying vector data and composing simple vector-only maps. ENVI also provides vector overlays on standard ENVI displays that include true vectorization of overlays in all windows, including the Zoom window. Full precision of vector data is maintained and pixellation is avoided. Vectors can be read from a variety of input files and new vector layers can be created and drawn in a Vector window or over images. Latitude/longitude and map coordinate information can be displayed while interactively tracking vectors. A Vector Information window allows display of attribute information in real-time as the cursor tracks each vector. You can query vector GIS attribute information directly to generate new layers of selected information with attributes. You can create ArcView shapefiles and associated .dbf attribute files and indexes, or DXF files from internal ENVI .evf format. New vector layers generated using ENVI's robust image processing capabilities, and changes made to vector layers in ENVI are easily exported to industry standard GIS formats.

ENVI Vector windows provide you with a way to view vector data such as USGS Digital Line Graphs (DLG), USGS DLGs in Spatial Data Transfer Standard (SDTS) format, DXF files, ARC/INFO Interchange files, and ArcView shapefiles. You can view, edit, and query attributes associated with ArcView shapefiles and can also create your own vector files and attributes. An ENVI Vector window consists of a vector display window or Image window and a Vector Parameters dialog that controls the appearance of the vectors and interaction with the vector attributes.

Cursor Functions in Vector Windows

Cursor and mouse functions in vector windows work differently than they do in ENVI display windows. Cursor functions in the vector windows change depending on the mode selected. The following table lists the functions of the mouse buttons when you place the cursor in a Vector window and the Cursor Query mode is active. See Controlling Cursor Modes for cursor functions in the other modes. More detail on these functions can be found in the following sections.

Use Help

Mouse Button Descriptions to bring up a dialog description of each mouse button.

Table 3-5: Function of Mouse Buttons in the Vector Window

Table 3-5: Function of Mouse Buttons in the Vector Window
Mouse Button	Function
Left Button	When layer is active (indicated by a check mark next to the layer name under Select Active Layer in the right-click menu) - Snap to a near active vector and track map coordinates and Latitude/Longitude. (The coordinates are shown at the bottom of the Vector window.) When layer is not active (no check mark appears next to the layer name under Select Active Layer in the right-click menu) - Pan the display by clicking at the edge of the window. (The Mode label at the bottom of the Vector window displays Pan with the direction of the pan when the mouse is near the edge of the Vector window.)
Middle Button	Zoom into an area by clicking and dragging to form a zoom box inside the Vector window. Decrease zoom factor with single click inside the window. Click while holding down the Shift key to zoom into the display centered on the cursor.
Right Button	Click to display the right-click menu.

Zooming in Vector Windows

Press and hold the middle mouse button at one corner of a box defining the magnify region and drag the corner to make the region the desired size.

Note
Click the middle mouse button while holding down the Shift key to zoom into the display centered on the cursor.

Release the middle mouse button. ENVI redraws the enlarged zoom region in the Vector window.

To zoom out use one of the following methods.

Using the mouse - Click the middle mouse button inside the zoomed region. The vector display steps backward through the previous zoom levels with one step per click.

Using a right-click menu - Click the right mouse button inside the Vector window and select Previous Range. The vector display steps backward through the previous zoom levels.

Select Reset Range from the right-click menu to reset all zooming and set the vector display back to the original range.

Panning in Vector Windows

To pan to another region in the Vector window, left-click near the edge of the Vector window. The Mode label at the bottom of the Vector window displays Pan and the direction of the pan when the mouse is near the edge of the Vector window.

Cursor Tracking in Vector Windows

If you are attempting image-to-map registration (see Registration), you need to find the location of your cursor. If vectors display in an Image window, ENVI reports the position of the cursor by displaying it in the Location text box of that window's associated Vector Parameters dialog. If vectors display in a Vector window, ENVI reports the position of the cursor in the bottom-left text box in the Vector window.

A check mark next to the layer name under Select Active Layer in the right-click menu of the Vector window indicates that a layer is active. When active, the vector cursor snaps to the nearest vector in that layer. When not active, no snap is applied and the cursor freely tracks position anywhere in the window. In either case, left-clicking and dragging in the Vector window causes the map coordinates of the cursor's location to be listed in Easting, Northing order in the lower right corner of the Vector window. Latitude and longitude are listed directly under the map coordinates.

Vector Options

Vector data often consist of multiple layers of vector data. For example, the following figure shows that the available vector layers include Cities, Counties, Roads, and States. Use the Vector options, which appears with a Vector window, to control the appearance of vector layers, to add new vectors, export vector layer coordinates for use in image-to-map registration, and to view, edit, and query vector attributes (see Working with Vector Layers for details).

Vector Attributes

Vector layers may have attributes associated with them. ENVI can read Shapefile attributes and interact with them. You can use the cursor to select vectors in the Vector window and highlight the associated attributes or select an attribute and highlight the associated vector. You can do a vector attribute query to create new vector layers with attributes selected using simple mathematical and logical operators. ENVI also allows you to edit the existing attributes or to add new attributes to vectors. Point attribute names can be plotted in the Vector window and point symbol sizes associated with attribute values (see Vector Attributes for instructions).