|ENVI User's Guide: Display Management|
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.
Follow these steps to display vector files in ENVI:
The Vector window appears with the selected vectors displayed (see Vector Options).
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.
To start a new empty Vector window and an associated parameters dialog, select Options Start New Vector Window.
To delete all the vector layers from memory, select Options Remove All Layers.
When vectors are deleted from memory, the only way to recover the layers is to read them from disk again.
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.
Use Convert Layer Projection to convert layers from one projection type to another.
For more information on converting projections, see Converting Map Projections.
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.
If you select more than one layer, the distance is from the pixel to any of the selected 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.
You can also create world boundaries by selecting Vector Create World Boundaries from the ENVI main menu.
.evffile 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
_hrfor 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
_usaappended to the root name.
Building layers from the high resolution database creates very large output files (~20 MB each).
The selected layers appear in the Available Vectors List.
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.
You can also create vector layers by selecting Vector Create New Vector Layer from the ENVI main menu (see Creating Vector Layers).
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).
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.
ENVI vector files can be converted to DXF using Vector Convert EVF to DXF (see Converting EVFs to DXF Files).
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:
EVF: evf name (record=n),
where evf name is the name of the input EVF layer and n is the record number from which the ROI originated.
EVF: evf name (attribute name=attribute value),
where evf name is the name of the input EVF layer, attribute name is the chosen attribute column name, and attribute value is the attribute value of the record from which the ROI originated.
To export vector layers to ROIs:
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.
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 (
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.
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.
Vector layers listed in the Available Vectors List are currently in memory. Use this procedure to save them to a file.
ENVI Online Help (August 12, 2005)