The Plot Cross Sections tool is the main way to visualize cross section data. Cross sections are displayed in profile view, across the river, perpendicular to flow. Multiple cross sections can be viewed simultaneously and several different types of reference lines can be included in the display.
The window is divided into three panes: The left pane contains the controls to select which cross sections are included in the view. The bottom pane contains summary metrics for each cross section currently being displayed. And the right pane contains the cross section plots themselves.
Cross Section Controls
Start by selecting one or more surveys for which you want to display. You can select multiple surveys by clicking the first desired item in the list and then holding down shift to click a second item. All surveys between the two items clicked will be selected. A discontinuous set of surveys can be selected by holding down the control key (CTRL) key while you click.
Pick the selection that contains the cross Selection that you want to view in the plot. If you need to create a new selection, you need to close the cross section plot tool before you can use the new selection.
Pick one or more cross sections from the bottom list using the same shift or control key technique described above. Cross section profiles will start to appear in the right pane once you have at least one survey and cross section selected.
Note that this bottom cross section list only contains the cross sections that occur within the currently selected survey(s) and selection above. If you are looking for a particular cross section and it doesn’t appear it is probably that it wasn’t surveyed in the currently selected survey(s) and/or doesn’t exist in the selection. visit the surveys and Selection tool to investigate whether this is true.
Cross Section Metrics
The bottom pane shows summary metrics for the cross sections that are currently displayed in the main plot area.
- Survey - name of the survey to which the cross section belongs.
- River mile - longitudinal position of the cross section along the river. River mile zero is downstream.
- Point count - total number of surveyed points along the cross section. i.e. the count of black dots in the figure above.
- Straight length (
D) - planimetric, 2D euclidean distance between the first and last surveyed point.
- Bed Length (
A + B + C) - sum of the lengths between each survey point along the cross section.
- CRP profile area (
E) - the profile area of the cross section after it is either extended up to, or truncated at, the construction reference plane. See the technical reference.
- Min Elevation (
F) - the absolute, vertical elevation of the lowest surveyed point.
- Max Elevation (
G) - the absolute, vertical elevation of the highest surveyed point.
- Average Elevation (
G - ((H/D)/2)) - the average elevation of all surveyed points.
- CRP Elevation (
I) - the absolute, vertical elevation of the newest CRP for this cross section.
- Min Offset - the smallest offset of any survey point along the cross section.
- Max Offset - the largest offset of any survey point along the cross section.
- Average Offset - the average of all offsets for surveyed points along the cross section.
Survey vessels commonly attempt to follow monumented cross sections (using GPS and/or navigation software), but the actual path that the vessel follows differs from the intended, monumented cross section. In these situations, an offset can be recorded that captures the planimetric, 2D, Euclidean distance of the point that was actually surveyed from the position on the monumented cross section that it represents.
The Plot Options tab (see below) enables the user to filter out survey points that possess an offset greater than a specified tolerance. This can be useful if several surveyed points possess excessive offsets.
Note that this main cross section plot tool is the only tool in the cross section viewer software that uses offsets and performs this filtering. All other tools uses all surveyed points for each cross section.
The currently displayed plot as well as the underlying data can be exported at any time. When exporting the data, the stations and elevations for all currently displayed selections are written to a comma separate plain text ASCII file.
The plot options tab contains several ways of controlling the cross section plot.
- Standard/comparison - this control is currently not operational. It does not currently alter the graph in any way.
- Y Axis - You can adjust the minimum and maximum values of the vertical axis on the main plot. Values are in the same units as the cross section elevation data.
- Offset filter - If the cross section data possess offset values, this control can be used to exclude survey points that possess an offset greater than the value shown (see graphic and explanation above).
- Line width - controls the thickness of the line used to draw all cross section profiles. Units are in screen display pixels.
- Reference stations - adds vertical lines to the plot at the relevant distances along the cross sections. Reference stations are managed using the main Data menu.
- Reference stages - adds horizontal lines to the plot at the relevant elevations. Reference stages are managed using the main Data menu.