SMS

Understanding Projections vs. Reproject

By aquaveo on December 18, 2019

Have you ever wondered what the difference between projection and reprojection is? Have you ever needed to convert a projection from one type to another in GMS, SMS, or WMS (collectively known as XMS)? The use of projections in WMS can be confusing, so the following should provide further clarification.

Specifying Projections

Projections can be associated with individual data objects, either in the object data file itself or in an associated *.prj file. If XMS cannot find a projection, the object will be left as "no projection," or, when new objects are created, XMS will assign the display projection to it. You can specify an object's projection by right-clicking on it and selecting Projection. Note that this projection must be the same as the original projection of the data; specifying an incorrect projection will result in data issues.

Reprojecting on the Fly

"Reprojecting on the Fly" occurs when datasets or objects from multiple projections are loaded into a project, where the x and y values would not otherwise overlap (i.e., the data would be displayed in two or more distinct locations). The different projections for these data will be "reprojected on the fly" to match the display projection such that the data objects will line up. Note that this does not change any *.prj files or the projections that are set for each object; it is an automatic function internal to XMS used for display purposes.

Converting a Projection

If you need to convert from one projection to another, this can be done by right-clicking on it and choosing Reproject. To use this command, the data must first have the correct projection specified. After choosing Reproject, the command will prompt the user to select a new projection, the data will be converted to the selected projection. If a *.prj file is associated with the object (such as a TIFF), reprojecting the object will change the *.prj file. Reprojection on the fly is usually sufficient for most applications. Please note that there are some limitations for reprojecting.

Reporject Dialog Example

Once the datasets are referencing their projection correctly, XMS should reproject them on the fly to match your display projection. If you don't have a display projection set, you can do so by selecting the Display menu and choosing Projection. At that point, if you would like to reproject your scatter(s) into the same projection as the display projection, you would be able to do so.

Now that you see the differences between projection vs. reproject try them out in XMS today!

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Tips for Feature Stamping

By jcreer on December 11, 2019

Have you ever needed to add an abutment, embankment, or other feature to your mesh and found it a struggle? We have some good news for you: SMS includes a function called Feature Stamping that is useful for this exact situation.

Feature stamping allows you to add man-made structures to an already created mesh by means of a stamping coverage.

Feature Stamping Example

You can find out more about this process in this wiki workflow.

There are, however, a few items to keep in mind when attempting to use the feature stamping tools. In this post, we’ll cover some of the most common, and how to troubleshoot them.

Make a High Quality Mesh

In order for feature stamping to be the most effective, it is necessary to enter them into a mesh that is already stable. Some items to look for include:

  • Making sure the mesh has enough detail.
  • Checking that the spacing between vertices isn’t too extreme in any portion.
  • Making use of the Redistribute Vertices tool.

You can find much more about creating quality meshes on here our blog.

Avoid Disjointed Vertices

Disjointed vertices are points in the scatter that have not been connected to triangles or quadrilaterals in the mesh. Feature stamping will fail if there are any disjointed vertices in the mesh.

There are two options for fixing this:

  • Find and delete all of the unconnected vertices.
  • Re-triangulate the mesh.
Keep the Stamping Features Short, Linear, and Independent

Feature stamping is usually linear, following a centerline.

If the structure is too large, or crosses over with other structures, it often has problems properly integrating with the mesh.

You can find examples here of when features are considered to be overlapping.

As long as your stamping features are reasonable in size and don’t interfere with each other, you should be able to successfully stamp your man-made features into the mesh.

Feature stamping is a very useful, but sometimes under-utilized, tool. Try out the feature stamping function in SMS today!

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Best Practices for 2D Hydraulic Modeling

By aquaveo on November 20, 2019

In SMS, designing a good 2D hydraulic model from the start gives the best results. A poorly designed model can give bad results, cause model errors, or even keep the model from converging. And while it may seem easy at first to design a good model, there are plenty of potential pitfalls that can come up if you are not careful.

The following tips, broken down into five areas, can help improve any model.

Terrain Data

Pay attention to your terrain data. You can't set up a good model without a good foundation, and terrain data is your foundation. There are four things you will need to spend time getting right:

  • Represent hydraulic controls accurately
  • Make sure you include channel bathymetry
  • Add breaklines where needed
  • Finally review the terrain surface for missing features
Terrain review
Mesh Development

Use an appropriate number of elements: size does matter, more is not always better. This is mainly because the time your model takes to render is a significant factor for any project. Element length should generally be equal to or greater than the flow depth, except for limited areas such as piers. When elements are too small, waves can form skewing the model results.

Quadrilatereal elements in meshes are often more stable than when using triangular elements. Once you have set your number of elements and length, confirm that hydraulic controls are represented in the mesh.

Lastly, review your mesh for quality.

Mesh quality review
Boundary Conditions

When determining the boundaries of your model, you will need to find two things. First look for the most constricted area when determining model limits. Second, find the furthest usable boundary location from the area of interest. A good rule of thumb for rivers: two floodplain widths up and downstream. Note that the width of the mesh should be greater than the maximum flood width.

Lastly, perform sensitivity analysis on boundary conditions.

Material Roughness

Be aware that Manning's n values for 2D model can be lower than 1D models. Be sure to calibrate your model. Essentially check your results to see if they are reasonable.

Model Execution and Review
  • Use the largest time step possible that gives you continuity and stability ( i.e. while still achieving a good solution).
  • Use monitoring points to verify steady simulation.
  • Use monitoring lines to verify continuity.
  • Review convergence parameters to confirm conservation of mass.

Following these tips can improve any model that uses a 2D mesh. Try them out in SMS today!

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Using the Prune Arc Tool

By aquaveo on October 30, 2019
The Prune Arc tool is relatively new to SMS, and we're excited to show you just how useful it can be.

The Prune Arc tool is similar to the smooth arc function in SMS. This Smooth Arc tool is useful when eliminating noise from a rough arc, and can make your variations more mathematically stable. This can be extremely handy in working with a model—especially in situations like coastal modelling, which are prone to busy edges. Unfortunately, smoothing an arc can also change the shape of the arc to the point where it no longer matches the actual coastline.

You may come across a situation where your imported arcs have a lot of unnecessary roughness or concave areas that you want to eliminate without redistributing your vertices along the rest of the arc.

If this is the case, the Prune Arcs function is just the tool for the job. This tool trims—or prunes—rough edges and outlying spikes without rounding or reshaping the rest of the arc. Specifically, it allows you to focus on smoothing one side of the arc. This is helpful in coastal modeling where there may be a small river mouth, a harbor, cove or other concave sections that you do not want to include in your model.

Prune arc example

Access the Prune Arc tool by doing the following:

  1. Use the Select Feature Arcs tool to choose the arc or arcs you wish to prune.
  2. Right-click on the selected arcs then, in the menu, select the Prune Arc(s) command.

This will bring up the Prune Arcs dialog box, from which you can choose your pruning settings.

There are two types of pruning that can be done: Constant and Spatially Varying.

  • Constant will prune everything within a specific measurement set by you. This measurement is in meters by default. The larger the number, the more dramatic the pruning will be.
  • Spatially Varying uses the numbers in a particular dataset to establish the parameters of the pruning. This dataset is chosen in the Prune Arcs dialog box.

Importantly, you must choose which side of the arc to prune. The sides of the arc are determined by the arc direction. So if the arc is moving south to north, the left side of the arc will be on the left side of your screen. If the arc is moving west to east, the left side with be towards the top of your screen. Make certain you are pruning the correct side of the arc.

Try out using the Prune Arc tool in SMS 13.0 today!

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