GRASS GIS Manual: wxGUI Vector Digitizer

Note: A new GRASS GIS stable version has been released: GRASS GIS 7.8, available here.
Updated manual page: here

wxGUI Vector Digitizer

DESCRIPTION
NOTES
REFERENCES
SEE ALSO
AUTHOR

DESCRIPTION

The vector digitizer is a wxGUI component intended for interactive editing and digitizing vector maps (see v.edit for non-interactive vector editing GRASS capabilities).

Note that only vector maps stored or generated in the current mapset can be opened for editing.

The digitizer allows editing of 2D vector features (points, lines, centroids, boundaries, and areas).

Vector features can be selected by mouse (bounding box or simply by mouse click, see select threshold in Settings→General→Select threshold), or by query (eg. by line length, see Settings→Query Tool).

STARTING THE DIGITIZER

The vector digitizer can be launched from Map Display toolbar by selecting "Digitize" from Tools combobox. Vector map is selectable for editing from Digitizer toolbar ("Select vector map" combobox, note that only vector maps from the current layer tree in Layer Manager are listed). The vector digitizer can alternatively be activated from the contextual menu in the Layer Manager by selecting "Start editing" on selected vector map in the layer tree, or directly from the Layer Manager toolbar icon

. The vector digitizer also can also be launched from the command line as a stand-alone application g.gui.vdigit.

CREATING A NEW VECTOR MAP

A new vector map can be easily created from the digitizer toolbar by selecting "New vector map" in "Select vector map" combobox. A new vector map is created, added to the current layer tree in Layer Manager and opened for editing. "Select vector map" combobox in the digitizer toolbar also allows easily switching between vector maps to be edited.

EDITING AN EXISTING VECTOR MAP

An existing vector map selected in the digitizer toolbar in the "Select vector map" combobox. This map is then opened for editing and added to the current layer tree in the Layer Manager. This "Select vector map" combobox in the digitizer toolbar also allows to easily switch between vector maps to be edited.

USING A RASTER BACKGROUND MAP

In order to digitize from a raster map, simply load the map into the Map Display using the Layer Manager. Then start digitizing, see below for details.

USING A VECTOR BACKGROUND MAP

The vector digitizer allows you to select a "background" vector map. Loading it within the digitizer is different from simply loading it via Layer Manager since direct interaction with single vector features then becomes possible.
Vector features may be copied from the background map by "Copy features from (background) vector map" tool from the "Additional tools" of the digitizer toolbar. Newly digitized vector features are snapped in the given threshold to the features from the background map.

DIGITIZER TOOLBAR

Digitize new point

Add new point to vector map and optionally define its attributes.

Digitize new line

Add new line to vector map and optionally define its attributes.

Digitize new boundary

Add new boundary to vector map and optionally define its attributes.

Digitize new centroid

Add new centroid to vector map and optionally define its attributes.

Digitize new area

Add new area (closed boundary and one centroid inside) to vector map and optionally define its attributes.

Move vertex

Move selected vertex of linear feature. Thus shape of linear feature is changed.

Add vertex

Add new vertex to selected linear feature (shape not changed).

Remove vertex

Remove selected vertex from linear feature. Thus shape of selected feature can be changed.

Edit line/boundary

Edit selected linear feature, add new segments or remove existing segments of linear feature.

Move feature(s)

Move selected vector features. Selection can be done by mouse or by query.

Delete feature(s)

Delete selected vector features (point, line, centroid, or boundary). Selection can be done by mouse or by query.

Delete areas(s)

Delete selected vector areas. Selection can be done by mouse or by query.

Display/update categories

Display categories of selected vector feature. Category settings can be modified, new layer/category pairs added or already defined pairs removed.

Display/update attributes

Display attributes of selected vector feature (based on its category settings). Attributes can be also modified. Same functionality is accessible from Main toolbar "Query vector map (editable mode)".

Additional tools

Break selected lines/boundaries at intersection
Split given vector line or boundary into two lines on given position (based on v.clean, tool=break).
Connect two selected lines/boundaries
Connect selected lines or boundaries, the first given line is connected to the second one. The second line is broken if necessary on each intersection. The lines are connected only if distance between them is not greater than snapping threshold value.
Copy categories
Copy category settings of selected vector feature to other vector features. Layer/category pairs of source vector features are appended to the target feature category settings. Existing layer/category pairs are not removed from category settings of the target features.
Copy features from (background) vector map
Make identical copy of selected vector features. If a background vector map has been selected from the Layer Manager, copy features from background vector map, not from the currently modified vector map.
Copy attributes
Duplicate attributes settings of selected vector feature to other vector features. New category(ies) is appended to the target feature category settings and attributes duplicated based on category settings of source vector features. Existing layer/category pairs are not removed from category settings of the target features.
Feature type conversion
Change feature type of selected geometry features. Points are converted to centroids, centroids to points, lines to boundaries and boundaries to lines.
Flip selected lines/boundaries
Flip direction of selected linear features (lines or boundaries).
Merge selected lines/boundaries
Merge (at least two) selected vector lines or boundaries. The geometry of the merged vector lines can be changed. If the second line from two selected lines is in opposite direction to the first, it will be flipped. See also module v.build.polylines.
Snap selected lines/boundaries (only to nodes)
Snap vector features in given threshold. See also module v.clean. Note that this tool supports only snapping to nodes. Snapping to vector features from background vector map is not currently supported.
Split line/boundary
Split selected line or boundary on given position.
Query tool
Select vector features by defining a threshold for min/max length value (linear features or dangles).
Z-bulk labeling of 3D lines
Assign z coordinate values to 3D vector lines in bounding box. This is useful for labeling contour lines.

Undo

Undo previous operations.

Redo

Redo previous operations.

Settings

Digitizer settings.

Quit digitizing tool

Changes in vector map can be optionally discarded when digitizing session is quited.

NOTES

Mouse button functions:
Left - select or deselect features
Control+Left - cancel action or undo vertex when digitizing lines
Right - confirm action

Dead (deleted) features are only marked as 'dead' in the geometry file but remain there and occupy space. Any vector module used afterwards on this vector map which really reads and writes vector geometry (so not g.copy) will write only features which are 'alive'.

Added or modified vector features are snapped to existing vector features (Settings→General→Snapping). To disable snapping set the snapping threshold to '0'.

If the digitizer crashes for some reason, the changes are automatically saved. Broken topology can be repaired by running v.build.

GRASS GIS uses a topological vector format, meaning that a common boundary of two polygons is only stored once. When digitizing polygons it is thus important to be able to only draw each boundary once. When drawing a polygon adjacent to an existing polygon, one has to first split the existing boundary at the points where the new boundary will be attached. Snapping should be set to ensure that the new boundaries are automatically attached to the chosen points.

REFERENCES

GRASS Vedit Library
Vector Database Management (Wiki page)

AUTHOR

Martin Landa, FBK-irst (2007-2008), Trento, Italy, and Czech Technical University in Prague, Czech Republic

$Date$

SOURCE CODE

Available at: wxGUI Vector Digitizer source code (history)

Note: A new GRASS GIS stable version has been released: GRASS GIS 7.8, available here.
Updated manual page: here

wxGUI Vector Digitizer

Table of contents

SOURCE CODE