Help:Glossary

This page contains a glossary of terms commonly used in XMS. Many of these terms have usage specific to XMS and may or may not coincide with how these terms are used elsewhere.

Typically the definition should correlate to the USGS definition.

A

annotations

model used to add notes or references to world or screen coordinates.

arc

sequences of line segments or edges, which are grouped together as a single "polyline" entity.

arc group

multiple arcs that have been grouped together so they can be selected at once.

B

bathymetry

the measurement of depth of underwater terrain.

borehole

a deep, narrow hole made in the ground, especially to locate water. Can contain either stratigraphy data or sample data or both.

boundary condition

a differential equation together with a set of additional constraint. Often abbreviated as BC.

breakline

a series of edges to which the mesh or scatter triangles should conform. A breakline is a feature or polyline representing a ridge, thalweg, or other shape to preserve in a surface made up of triangular elements or scatter set. In other words, a breakline is a series of edges to which the mesh or scatter triangles should conform to, i.e., not intersect.

C

CAD

CAD (computer-aided design) is the use of computers for design.

centerline

arc that represents the direction of a river from upstream to downstream.

Clough-Tocher

an interpolation technique is often referred to in the literature as a finite element method because it has origins in the finite element method of numerical analysis. Before any points are interpolated, the points are first triangulated to form a network of triangles. A bivariate polynomial is defined over each triangle, creating a surface made up of a series of triangular Clough-Tocher surface patches.

compass plot

plot representing temporally varying vector data.

contour

a curve along which the function has a constant value.

coverage

groups of feature objects and attributes in the Map module.

cross section

arcs used to extract elevations in SMS and WMS. In GMS, cross sections are flat surfaces used to visualize the subsurface.

culvert

a structure that allows water to flow under a road, railroad, trail, or similar obstruction.

D

DEM

a digital elevation model is a representation of a terrain's surface created from terrain elevation data.

dialog

a window that pops up after a command is executed. May also be called a window, tool, or editor.

E

element

used to describe the area to be modeled. Elements are formed by joining nodes. May be one dimensional, triangular, or quadratic.

extrapolation

in the context of SMS, extrapolation is an optional feature to estimate a value when a scatter set does not bound the data to which it is being interpolated.

F

feature object

patterned after Geographic Information Systems (GIS) objects and includes points, nodes, arcs, and polygons. Feature objects can be grouped together into coverages, and each coverage defines a particular set of information.

feature stamping

is a tool that can be used to insert man-made structures into a natural topography or bathymetry set.

flow trace

animation technique used to visualize vector fields.

G

GIS

a GIS, or Geographic Information System, is a computer system used for storing, organizing, managing, manipulating, analyzing, and visualizing spatial or geographic data.

GMS

GMS (Groundwater Modeling System) is a program for building and simulating groundwater models.

graphics window

the main portion of the XMS program that gives a visual representation of the project.

groin

a rigid hydraulic structure built from an ocean shore (in coastal engineering) or from a bank (in rivers) that interrupts water flow and limits the movement of sediment.

H

HY-8

culvert analysis program developed by the Federal Highway Administration.

hydrograph

a graph showing the rate of flow (discharge) versus time past a specific point in a river, or other channel or conduit carrying flow.

hydrography

the science that measures and describes the physical features of bodies of water and the land areas adjacent to those bodies of water.

I

IDW interpolation

inverse distance weighted (IDW) interpolation assigns values to locations based on the values at nearby locations. As the distance from one location to another increases, the influence of that location on the value assigned to the other decreases.

interpolation

a method of computing values at points within the range of other points with known values.

isosurface

a surface of constant value extracted from a 3D dataset.

J

jackknifing

a special type of interpolation which can be useful in analyzing a scatter point set or an interpolation scheme.

jetty

a structure that projects from the land out into water.

K

Kriging

a method of interpolation named after a South African mining engineer named D. G. Krige who developed the technique in an attempt to more accurately predict ore reserves. Over the past several decades kriging has become a fundamental tool in the field of geostatistics.

L

LandXML

a generic, text-based file format used to store spatial data.

LiDAR

light detection and ranging.

M

macro

button that executes a commonly used command.

menu

a list of commands. Can be found at the top of the XMS interface or by right-clicking on items.

mesh

a mesh consists of nodes that are grouped together to form elements. These nodes and elements define the computational domain of the numerical model. A numerical simulation requires a geometric definition of its domain. For many numerical analysis codes, this definition is a mesh.

mesh element

mesh elements are used to describe the area to be modeled. Elements are formed by joining nodes. The element types supported vary from model to model.

mesh node

a mesh node is the basic building block of elements in a mesh. A node consists of a location (X,Y) with an associated elevation. Other dataset values can also be associated with a node. The density of mesh nodes helps determine the quality of solution data and can be important to model stability.

mesh nodestrong

a collection of nodes can be formed into a nodestring. Nodestrings are most commonly used to assign boundary conditions such as a flowrate or water-surface elevation. Nodestrings can also be used for mesh renumbering, forcing break lines, and boundary smoothing. Finally, a nodestring can store attributes pertinent to a location such as the total flow nodestring.

MODFLOW

a 3D, cell-centered, finite difference, saturated flow model developed by the United States Geological Survey.

N

node

define the beginning and ending XY locations of an arc.

nodestring

a collection of nodes.

O

observation

display the variation of one or more scalar datasets associated with a mesh or grid.

P

plot axes

a set of ruled lines oriented in either the world coordinate system or the grid coordinate system.

point

XY locations that are not attached to an arc.

polygon

a group of connected arcs that form a closed loop.

project explorer

the portion of the interface that lists datasets and components of the project.

projection

refers to a map projection like UTM. In XMS software, a projections are associated with the project and individual data objects.

Q

quadtree

a two-dimensional space partitioned by recursively subdividing it into four quadrants or regions.

R

raster

data (usually elevation) stored in pixels.

raster catalog

a table that allows assigning attributes to rasters.

RST

a file which can be created by SRH-2D that can be used as initial conditions for an SRH model run.

S

segment

the portion of an arc between two vertices or a node and a vertices.

simulation

a collection of objects used to define an specific model run. The objects included in each simulation may vary depending on the project parameters and the model being used.

size dataset

defines the desired spacing of nodes in a spatial fashion.

SMS

SMS (Surface-water Modeling System) is a program for building and simulating surface-water models.

spectral energy

represents energy densities at discrete values over a range of angles and a range of frequencies for a given wave condition.

SRH-2D

two-dimensional hydraulic, sediment, temperature, and vegetation model for river systems developed by the Bureau of Reclamation.

SRH-2D monitor line

an internal polyline which may be used to monitor the total flow discharge through it. Monitor lines are applied the model to determine the flow and sediment flux across the lines at specified locations in the model. SRH-2D creates a file for each monitor line that details the bed and water-surface elevations, the flow, and the sediment flux across the lines. The monitor lines can be used to determine when the model reaches steady state conditions. For example, by comparing the predicted water-surface elevations over time and at various locations along the reach, the user can determine when the water-surface elevation reaches a steady state condition.

SRH-2D monitor point

a monitor point is used to gather specific information for that location at all time steps. Information calculated by SRH-2D at a monitor point includes position in the X and Y direction, bed elevation, water elevation, water depth, X direction velocity component, Y direction velocity component, velocity magnitude, Froude number, and shear stress.

SRH-2D simulation

a collection of objects used to define an SRH-2D model. An SRH-2D simulation must include a 2D mesh, boundary condition coverage, and material coverage. It may also include a sediment materials coverage, a monitor point coverage, and an obstructions coverage.

surfer

a contouring and 3D surface mapping software program.

T

TECplot

visual data analysis program which may be used to visualize results from the SRH-2D program.

time series

a series of values of a quantity obtained at successive times.

TIN

a triangulated irregular network that is a digital data structure used in a geographic information system (GIS) for the representation of a surface.

U

UGrid

a module that uses an unstructured grid.

V

variogram

a description of the spatial continuity of the data.

vertex

XY locations along arcs in between the beginning and ending nodes.

W

weir

a barrier across a river designed to alter its flow characteristics.

WMS

WMS (Watershed Modeling System) is a program for building and simulating watershed models.

X

xy series

curve defined by a list of x and y coordinates.

Z

zpts

A point with elevation, or vertical geometry, data attached to it. Also sometimes zpt.