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Annotations

Annotations

Annotations are text, vectors, or graphics used to highlight features, details, or points of interest within an image. Use the Annotation toolbar tools to work with annotations. ENVI supports ENVI annotation files (.anz, .ann) as well as NITF annotation segments. You can save annotations to new .anz files.

See the following sections:

Create and Save an Annotation Layer


  • Create a new layer by selecting File > New > Annotation Layer from the menu bar.
  • Select a Source Data file when creating an new layer to define the new layer’s extents and map projection using an existing file.
  • When the layer has been modified, the icon next to the layer name in the Layer Manager becomes shaded Dirty annotation layer icon. The icon shading is removed once the layer is saved.
  • Save layer changes by right-clicking in the Image window view and selecting Save.
  • Save layer changes to a new file by right-clicking in the Image window and selecting Save As. Also use Save As when: saving a new layer for the first time, if you edited a NITF annotation segment, or if you are saving an ENVI .anz file to a new filename.
  • To hide an annotation layer in a view, disable the check box for that layer in the Layer Manager. To show the layer, enable the check box.
  • To remove an annotation layer from the Layer Manager, right-click on the layer and select Remove. This removes the layer from the Layer Manager, but the file remains open and you can access it for redisplay from the Data Manager.
  • To rename a layer, right-click its name and select Rename Item. Enter the new name in the Rename Item dialog and press the Enter key to accept it or press the Esc key to cancel. (Linux and Macintosh users should click the green check icon to accept the new name or click the red X icon to cancel.)
  • If you have multiple views displayed, you can drag-and-drop annotation layers from the Layer Manager to any one of those views in the display or to the corresponding view icons in the Layer Manager. This creates a copy of the layer(s) to populate the views.
  • If you open an OGC WMS raster layer that contains a legend, the legend displays in the Layer Manager. To create an annotation object from the legend that you can overlay on the image, right-click the layer name and select Load Layer as Annotation. This is useful, for example, in creating a Powerpoint presentation from the view.

Add Annotations


Annotation types include text, symbol, polyline, polygon, rectangle, ellipse, arrow, image, classification legend, color bar, and scale bar. Here are some general tips for adding annotations:

  • In the active layer, click the Annotation drop-down from the toolbar and select the annotation tool type, then click where you want to add the annotation. Draw the annotations. See the Text, Polylines and Polygons, Classification Legends, Color Bars, and Scale Bars sections below for specific instructions about these annotation types.
  • Click and drag to move an annotation to a different location.
  • Click and drag on a selection handle (indicated by a cyan-colored square) to resize an annotation.
  • To unselect one or more annotations, right-click and choose Clear Selected. Or, press the Esc key.
  • Symbol, ellipse, rectangle, and image annotations are initially drawn orthogonally to the display axes, regardless of the orientation (rotation) of the underlying data layer.

To copy and paste annotation items after creating them, follow these steps:

  1. Use the Select button to select one or more annotation items. Use the Ctrl or Shift keys to select multiple items, or draw a box around multiple items to select them.
  2. Right-click and select Duplicate Selected. The selected items are copied to the view.
  3. Click and drag to move the new items as needed.

The following sections provide details about specific annotation types.

Text

  • Text annotations are initially drawn horizontally with respect to the display.
  • To create superscript text, press the Ctrl+U keys and type the text.
  • To create subscript text, press the Ctrl+D keys and type the text.
  • To return to regular text from superscript or subscript, press the Ctrl+N keys.
  • To insert a line break, press the Ctrl+Enter keys.
  • To add four spaces between letters, press the Tab key.

Polylines and Polygons

  • Create polylines or polygons by clicking and dragging to draw them, or click at intervals to add vertices one at a time.
  • To draw a square or circle, with the Rectangle or Ellipse tools, press the Ctrl key as you click and drag.
  • Use the right-click menu options to accept vectors when they are drawn.

Classification Legends

Follow these steps:

  1. Select Legend from the Annotations drop-down menu in the toolbar.
  2. Click on a location in the Image window where you want to display the legend.
  3. When the File Selection dialog appears, select a classification image from which to create the legend. Click OK.

You can edit the class names displayed in the legend. Double-click the Legend annotation item in the Layer Manager to display the Edit Properties dialog. Click inside of the Legend Names field and click the arrow icon. Edit the legend annotation items as needed. This does not change the class names in the classification image, only the class names displayed in the legend.

Color Bars

Follow these steps:

  1. Display a single-band greyscale image.
  2. Right-click on the image layer in the Layer Manager, select Change Color Table, and select a predefined color table.
  3. Select Color Bar from the Annotations drop-down menu in the toolbar.
  4. Click on a location in the Image window where you want to display the color bar.
  5. You can edit the labels that appear under the color bar. Double-click the Color Bar annotation item in the Layer Manager to display the Edit Properties dialog. Click inside of the Labels field and click the arrow icon. Edit the labels as needed.
  6. To retain the same scale for the color bar as you zoom in or out, set the On the Glass property to True.

Tip: The !M£!X string represents the ≤ character, and the !M3!X string represents the ≥ character. Different system fonts may render these characters differently.

If the view contains more than one single-band image layer, the color bar annotation will be associated with the top-most layer. If the color table or stretch type changes in the image layer, the color bar annotation will update accordingly. If you remove the image from the display, the color bar will still remain but will use the last known color table and stretch type.

Scale Bars

Scale bar annotations initially show distance in the units of the current base projection. For example, if the base projection is UTM Zone 13 (WGS-84), the scale bar distance is in meters. If the current base projection has angular units such as Geographic latitude/longitude, ENVI converts the units to meters for the scale bar.

  • To change the default units of the scale bar after you add it, double-click the annotation item and change the Units in the Edit Properties dialog.
  • The Scale on Zoom property is not available for scale bar annotations.
  • To adjust the length of the scale bar, choose one of the following options:
    • Modify the Increment property value.
    • Modify the Length property value, in pixels. Modifying the Length will update the Increment so that the scale bar fits within the designated length.
  • The scale bar distance is approximate when used with datasets that are in an RPC or pseudo spatial reference. The default units are meters.
  • When a scale bar annotation is used on an image with a geographic projection, the distances are calculated for the center latitude of the image. If the image spans more than a few degrees of latitiude, this scale bar representation will only be accurate around the center of the image and could vary greatly along the edges. For this reason, we do not recommend using the scale bar annotation on a global geographic image.

Delete Annotations


  • To delete annotations in the active layer, click the Select tool.
  • Select an annotation by clicking on it.
  • Select multiple annotations by using Ctrl+click, or by drawing a box around the items.
  • Right-click and select Delete Selected.
  • To delete an annotation you are creating and to start again, press the Esc key.
  • Right-click on an annotation layer in the Layer Manager and select Revert to clear all annotation item changes and to return the layer to the state it was in after it was last saved.

Change or Create Properties for New Annotations


  • You can change the properties of annotation items after you create them. Double-click the annotation item you want to modify in the Layer Manager, or right-click on it and select Properties. You can also click on the annotation item in the Image window view, then right-click and select Properties. The Properties dialog appears, listing settings specific to the annotation item type.
  • You can also change the default properties of annotation items before you create them. Use the ENVI Preferences dialog for this. See Annotation Preferences for details.

Affix Annotations to the Display


You can affix certain annotation items to the display so that they remain stationary while you zoom, pan, and rotate. See On the Glass Annotations Background for details.

Set the On the Glass property to True for the selected annotation item. ENVI automatically sets the Scale on Zoom and Rotate with View properties to False.

You can also right-click on the New Annotation item in the Layer Manager and enable one of these options:

  • On the Glass
  • Set "Scale on Zoom" to True (ignored if you enable On the Glass)
  • Set "Scale on Zoom" to False (ignored if you enable On the Glass)

Scale bar annotations do not have a Scale on Zoom property.

The icons for these annotation items are updated in the Layer Manager to indicate that they are on the glass; for example:

Zoom Options


  • To zoom to the full extent of a annotation layer, right-click on the layer name in the Layer Manager and select Zoom to Layer. This centers and displays the entire layer.
  • Selecting Full Extent from the Zoom drop-down menu or clicking the Zoom to Full Extent button in the main toolbar zooms to the combined extents of all layers for the current view.
  • If an annotation layer is georeferenced, the Zoom To drop-down list in the main toolbar displays options for Map Scale:

  • To specify whether or not to scale annotation items as you zoom in or out of the display, right-click on an annotation folder in the Layer Manager and select an option:
    • Set "Scale on Zoom" to True: The size of all annotation items in the selected folder will increase or decrease accordingly when the zoom level increases or decreases.
    • Set "Scale on Zoom" to False: The size of all annotation items in the selected folder remains the same, regardless of the zoom level.
  • You can also specify the Scale on Zoom preference item for text and symbol annotations, using the ENVI Preferences dialog.
  • To jump to the center of an annotation item, right-click on the item name in the Layer Manager and select Go To Item.



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