From the Rectification Control Points module in GTK+ GRASS the user can edit and manually enter control points.
Rectification Control Points
From this menu the user can:
- Turn control points on or off.
- Highlight the selected control point on the display.
- Check the Root Mean Square (RMS) error for the selected points.
- Manually enter known control points.
- Automatically project manually entered geographic coordinates to the users coordinate system (e.g. UTM).
This is a useful option for selecting geographic graticules on scanned maps.
The control points can be saved to a re-loadable XML points file. The XML file includes the image name, location and format, plus the complete list of control points. Using this format the image and control points can be easily re-loaded in a single step. The following is a sample control points XML file …
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A rectification Control Points module is added to the GTK+ GRASS Interface to make selecting and manipulating control points easier.
Image Rectification Window
The Control Points window opens in the GRASS Interface, as a special, split-pane, tabbed window. Users can select rectification control points for a GRASS raster file or an external image. Control points are saved to an XML file with optional output to a gdal_translate compatible file.
Features
The features for the Control Points Rectification module include:
- Control point selection for both GRASS rasters and external image files (TIFF, PNG, etc).
- Image file name and type, plus selected control points saved to a simple XML file.
- Control points selection from existing GRASS rasters and vectors or manually entered points.
- Control points manually entered from geographic coordinates or from the user’s projection coordinates (eg. UTM).
- Edit menu that displays RMS for selected points based on the chosen rectification order.
- Edit menu that lets users turn control points on or off.
- Predicted location for a selected point that displays in both panes to help users locate control points.
- Full zoom and pan functions for both panes in the rectification tab window.
The GTK+ GRASS Interface 3D View lets the user save a keyframe animation directly to a supported animation format. The 3D view uses the GRASS ogsf library to render an animation. If the GRASS ogsf library has been built with the optional FFMPEG library, movies can be directly rendered to any supported format.
Save Keyframe Animation Dialog
If FFMPEG support is not available, the animation can be saved as individual images.
By default, the animation is rendered off-screen. The user can optionally turn this off and render the animation in the current 3D View. The advantage of off-screen rendering is that other windows and screen-savers do not interfere with the saved animation.
The animation dialog shows the rendering progress by frame number.
The GTK+ GRASS Interface uses a simple XML interface to save the 3D state, keyframe animations, and run scripts.
XML State File
The 3D View module uses a simple XML format to save and load the 3D state. Supported fields include view position, lighting, and loaded GRASS objects (eg. raster). A sample script might look like the following:
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The GTK+ GRASS Interface supports the following overlays in the 3D View:
- Scalebar.
- Cutting Plane.
- Location Map Inset.
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Introduction
The GTK+ GRASS Interface can be built with an optional port to the GRASS ogsf library providing 3-D visualization support. This requires the user to install GtkGLExt, an OpenGL extension to GTK+ 2.0.
Screen shot of the GRASS Spearfish data set in 3-D view
The 3D View is loaded as a special tab in the Map Display. The 3D View is created with the GRASS settings (i.e. region). The user can easily switch between loaded map views and the 3D View.
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Map images can easily and quickly be saved from the GTK+ GRASS GUI. Saved images include all currently selected objects in the display list.
The map is saved by default to a PNG image at the same size as the display canvas. Other image formats supported by GTK+ will be added.
A second image save option is available to save map images as a scaled PNG image. The user is prompted to set the display width in pixels, of the output image. This option can be used to output map images at the current GRASS resolution, which can in turn be encoded to GeoTiff files or GDAL compatible files.
Note: The scaled image output is dependent upon system memory.
The right pane of the GTK+ GRASS GUI displays several user controlled Map Layers. The map layers can be added or removed at any time. Each map layer has its own associated GRASS Region, and display list (previous post). To optimize drawing speed, the GTK+ GRASS GUI uses its own internal drawing routines for GRASS files and decorations. This may be changed with the new display used in GRASS7.
Display options include the usual interactive zoom window, zoom/out, and pan. The GRASS region can also be manually edited. The region can also be set to a raster or vector from the GRASS file selection view.
Display Toolbar
The map view can be maximized to fill the window, overriding the current GRASS region.
The position can be queried and captured, features can be measured, plus rasters and vectors can be queried from the display.
Display overlays (decorations) include:
- Raster colorbar.
- Vector legend.
- Scalebar.
- Grid.
- Geographic grid.
- Compass rose.
