Drawing of polygons, rectangles and lines can be used to select areas or to modify an existing selection.
The selection can be drawn over either the DSM or the imagery. It will appear in both windows.
Press P to enable the polygon drawing tool (or: Within the Home tab on the Tools panel click the polygon drawing tool)
Hold Shift+Left-Click on the mouse button to draw a polygon
Hold Shift+Left-Click on the mouse button add additional points to the polyon.
Press Shift+Plus key to add the drawing as a selection (or: Go to Selection, panel Modify and press Add)
Draw other polygons by holding Shift+Left-Click mouse button and Add them to the selection
If a point in the polygon is set incorrectly while drawing it can be removed by pressing Shift+Backspace
and the drawing can be continue
To clear a selection press the Esc key
The picture below shows the displayed DSM and imagery of Boston downtown including selections over the public parks.
The selection of the two parks in the center (location: -71.0675680(°E), 42.3544870(°N)) appear in a checkered pattern over the data.
To center the dataset over the parks:
Go to the Home tab and the View panel and press Go To and enter the coordinates.
Zoom in with the wheel mouse.
The park along the river (upper left part of the area, cursor position) is just surrounded by a polygon but
not yet added to the selection. It is highlighted in green and will appear checkered after pressing Add.
The Flood Fill Tool is an excellent, semi-automated tool to select large areas in a very efficient manner.
Large areas of equal and similar pixel values can be selected by one click on the data layer being filled upon
according to the parameters defined in the Flood Fill Options.
Press F to enable the Flood Fill tool (or: Within the Home tab on the Tools panel click the Flood Fill tool)
Within the Selection tab on the Flood Fill Options panel set the following selection parameters:
Type: select Imagery as the raster layer used for the filling
Mode: select Tolerance (+/-)
Tolerance: use 10. This selects all connected pixels with pixel values of +/-10 of each R,G,B channel.
Action: select Add. Result will be added to any existing selection or a new selection will be created.
Connectivity: select 8-way
Max. Radius: enter 1000.00 m to select all similar pixels within a radius of 1000.00m
Press Shift+Left-Click on an area of similar color in the imagery, e.g. water, and the area around the pixel you clicked on
will be selected.
Repeat last step until all water areas are selected
The picture shows the cursor positions where the first mouse click was done and the area which was filled accordingly.
Areas can be excluded from selections. This is of interest in case of modification of an existing selection or
as a step in the selection process when e.g. the whole data set is selected first followed by the exclusion of specific areas.
To exclude an area from the selection of the whole data set:
Press Ctrl-A to select the whole data set
Press P to enable the polygon drawing tool
Hold Shift+Left-Click mouse button to draw a polygon around the area to be excluded
Press Shift+Minus key to exclude the drawing from the selection
(or: Within the Selection tab on the Modify panel and click Subtract)
Press Shift+Esc to clear the drawn polygon, but maintain the selection
The picture below shows the result of public park areas excluded from the selection of the whole Boston data set.
The two parks in the center are cleared from the selection. The park along the river
(upper left part of the area, cursor position) is just surrounded by a polygon but not yet subtracted from the selection and
is highlighted in green. It will be cleared from the selection after pressing Subtract.
Selection can be made based on pixel values or elevation values. This can be used to select all regions of values within a range.
To identify missing pixels, "no data" and "invalid data" (voids) a specific pixel value or a range of values can be selected.
In the following example, all "no data" areas will be selected under the assumption that the pixel value is unknown.
Usually, the pixel value of "no data" is -32767.0 or -9999.0.
Within the Selection tab on the Modify panel click Select Values
Set the following parameters in the dialog windows and press Ok:
Select data set: bostonDSM-1m
Select data: DEM
Enter comma separated ranges for values to select (e.g. 1,2-3,5): Ex. -100000--500
The picture shows all selected voids as the checkered pattern over water and land.
The voids can be filled in a further process step. E.g.:
Within the DEM tab on the Void Fill panel select Kernel → Inverse Distance Weighted to fill small voids by interpolation
Within the DEM tab on the Void Fill panel select Triangulation to fill larger voids