SG3d UPDATES

Documentation for new features specific to the latest version of SG3d for Floating Point/Null Value GRASS, which also incorporates a multiple attribute site format.

Floating Point/Null Value changes

All raster maps are now read as single precision floating point maps for loading into SG3d. Null values are noted and when drawn, the surface has gaps where there were NULLS, as in this example image. For backward compatibility, it is still possible to turn on "no zeros" to prevent the drawing of the surface at zero data areas. MASKs should work the same as they always have, since Floating Point GRASS reads masked area as NULL.

Support for visualization of 3d point data in site lists

For visualization purposes, point data is often used to derive an artificial surface or a volume from which isosurfaces may be calculated. Such data extrapolation and interpolation is also necessary for modeling purposes to produce input data for models that work with grids or volumes. Better visualization of point data for comparison to derived surfaces at various stages of the modeling process allows the researcher to better understand and verify the model. Building on recent improvements to the GIS library that work intelligently with spatial site data containing multiple attributes and more than two dimensions, visualization tools have been improved to allow multiple attributes/dimensions of point data to determine the shape, size, color and orientation of solid 3d markers as well as the 3d position. Additional tools have been developed to allow selection and display of a subset of sites from a larger file based on ranges of values for various attributes of each site. See also: New GRASS Library Functions, d.siter, d.sites.qual, s.info

Given a value for an attribute of the data at a particular site, visualization is accomplished by mapping the value to one or more characteristics of the marker. For each data attribute, SG3d allows a transformation consisting of an add_value and a multiply_value which converts the data value to visualization units (vis_value = (add_val + attribute_val) * mult_val). In the case of color, three attributes (representing red, green, and blue components) may be used to map a single characteristic, color by selecting the Read RGB toggle button. SG3d expects values in the range 0.0 to 1.0 to represent color when using this option. If a single identifier is entered in the fields: entry box, then a grey shade will be calculated from the attribute, otherwise three identifiers must be entered to specify which attributes should represent the red, green, and blue components of color, respectively. If Use category or Use value for color are selected, the existing GRASS color lookup functions are used for the transformed value, according to the color table as represented by a specified color (raster) file. GRASS only provides color lookup for raster data so you may have to create an empty raster unless you can use a color table from an existing raster. The characteristic of variable shape is accomplished by having an "alternative" size field which is used to scale the marker vertically.

"Info" button: Selecting "Info" prints to the text window a summary of what attribute fields, categories, dimensions, and string fields are present in the current sites file. Labels are printed for each field if present and attribute fields are numbered in the order they exist in the file. This is the number you would use to identify the field for use in visualization (see below).

Identifying site data elements to SG3d: On the new sites panel, for each visual characteristic of the marker there are text entry fields to identify which site field you want to use for that characteristic. Legal values for this entry are:

The numbers 1-N, where N is the number of double precision site attributes present.
The letters n,N,s,S,y,Y which all represent the northing coordinate
The letters e,E,w,W,x,X which all represent the easting coordinate.
The letters z,Z which both represent the 3rd dimension.

To use a category value instead of an attribute, choose "Use category"

Support for custom labeling of 3d point data in site lists

The new label panel includes the capability to automatically extract and place labels from a sites file. In addition, a set of proportion values from the sites file may be used to generate piechart labels for each site. Labelling is performed by selecting the type of label desired and then selecting the Label Sites button.

The in box check box applies to any of the site labels - it will draw a grey-shaded box which contrasts to the color chosen for the label before writing the label within the box, ensuring legibility of the label. Any combination of category, string, or value information may be used for the label. The label string will be created using first any category information (if the category checkbox is selected), then any string information (if the strings checkbox is selected), then any double attribute information (if the values checkbox is selected). Multiple fields may be requested in arbitrary order by entering text in the fields: entry box such as:

1 2 (fields 1,2)
1,2 (fields 1,2)
3-1,4 (fields 3,2,1,4)
N,2 1 (northing, then fields 2,1)

Commas or spaces may be used to separate field identifiers. When written to the label string, multiple fields are separated by spaces. The number in the precision entry box specifies how many decimal places to display when using double precision attributes as labels.

Using the format described above, multiple fields may be specified in the fields: entry box with the piechart box checked to produce piechart labels such as those in the example (click on image for larger image), which was drawn using settings as indicated by this image of the panel. Colors for the pie wedges are selected by using the "custom" colors from the color bar, in reverse order (right to left), then proceeding with the constant colors from the color bar if there are more than 5 ratio fields. Therefore, to change the colors, edit the "custom" colors by selecting set (next to the color bar). Size of the piechart probably ought to be controlled by setting font size, but instead it is currently implemented so that you must use the size slider on the Sites panel. Settings at the top of the Label panel are used to determine font size and color for all labels, including those used to label pie wedges when label values is selected. Double precision values in the sites file used to generate piecharts should range from 0.0 - 1.0 and the sum of those used should not be greater than 1.0. Note that precision does not affect the wedge labels; they are always rounded to the nearest whole percent.

Site labels are not drawn for sites which would lie on a masked portion of the surface.