Projections
| Related Versions | |
|---|---|
| GMS | v7.0 |
| SMS | v10.1 |
|
version note | |
"Projection" refers to a map projection like UTM. In XMS software, a projections are associated with the project and individual data objects.
Starting with SMS 11.1 and GMS 9.1, the XMS software works on the concept of a "Display Projection". This is the projection the user is working in. Each geometric object loaded into the XMS package, such as a Scatterset, DEM, grid or mesh, also has an associated projection. These two projections may not be the same. If the two projections are compatible (i.e. it is a viable option to convert from one projection to the other), the XMS package will convert the data from the object projection to the display projection, just for display purposes. This is referred to as "Project on the fly". The data itself maintains the values associated with the object projection so when the XMS package saves a project, the data files are not modified.
Alternatively, data can be reprojected from one projection to another, actually changing the data values that will be saved as part of a project. This is done by right clicking on the geometric object in the project explorer (data tree) and selecting the "Reproject..." command. The SMS package includes a feature to reproject all data from whatever projection the data is currently in to a single projection using the "Reproject All..." command in the Display menu.
XMS software utilizes the Global Mapper (TM) library which supports hundreds of standard projections.
Previous XMS software versions referred to projections as "coordinate systems" and reprojection as "coordinate conversion".
Contents
Display Projection
The current projection, or the projection currently associated with the project, can be specified via the Edit|Projection menu command. Changing the projection does not alter the XYZ coordinates of the project data.
No Projection (Previously Local Projection)
Many numerical models work in local or model space, and don't care how that system relates back to global coordinate systems (UTM, State Plane etc.). XMS software allows for this using a local/no projection option. This is standard practice when building a numerical model of a flume test. In this case, the display project would be set to local or no projection. The units of the model are then specified as part of the projection. If the display projection is in this mode, no global projections are allowed on individual objects.
(Note: when the display projection is set to No Projection or Local Projection, the data may still be referenced to a projection. The display projection can be changed to reflect that projection if desired.)
Reproject on the Fly
When data from multiple projections were loaded into and XMS application in the past, they would not overlay and the display would show data at two distinct locations.
Reproject
Reprojecting means to convert data from one coordinate system to another. For example, a 2D mesh representing the ground surface may have XYZ coordinates in a UTM system and they need to be converted to a State Plane system to be consistent with other data. Reprojecting usually results in the XYZ coordinates of the data changing, although conceptually the data is in the same place with respect to the Earth, just in a different coordinate system.
There are three basic reprojection tasks that you can do:
- Reprojecting the entire project from one system to another
- Reprojecting one object from one coordinate system to the project coordinate system
- Single point reprojection, which allows you to enter the XYZ coordinates for a point in one projection and see what the new coordinates would be if the point was reprojected to a different projection.
Either operation brings up a dialog with two projections specified. On the left, the "Convert From" projection defines the projection the data is currently in. On the right, the "Convert To" projection defines the projection the data will be in after the operation.
Reproject everything
Reprojecting everything can be done by selecting the Edit|Reproject menu command. This will convert all the data loaded into the XMS application from one projection to another. In this operation, the "Convert From" projection (left side of the dialog) is dimmed by default. The user selects a new projection on the right side that all data in the application will be converted to. This operation changes the "current" projection that is being used by XMS to the newly specified "Convert To" projection.
Reproject object
This command is done on a specific geometric object (grid, mesh, scatter set, ...) by right-clicking on the entity in the Project Explorer. The object is reprojected from some projection into the current projection being used by the XMS application. In this operation, the "Convert To" projection (right side of the dialog) is dimmed by default because it represents the current projection used by the project. It is assumed that the desire is to reproject data from another projection into the current projection. The current projection is not changed in this operation.
Single Point Reprojection
Single Point Reprojection allows you to enter the XYZ coordinates for a point in one projection and see what the new coordinates would be if the point was reprojected to a different projection. It also lets you create a feature point at the new location. This operation is accessed via the Edit|Single Point Reprojection menu command. It's also available in the Register Image dialog.
Restrictions
Some reprojections are not allowed, such as reprojecting between a NAD and non-NAD system. A warning is issued when the reprojection is not allowed.
Supported Projections
XMS software utilizes the Global Mapper (TM) library which supports hundreds of standard projections.
| Projections | |
|---|---|
| UTM: | Africa • Asia • Australia • Europe • North America • South America |
| State Plane: | Alaska • Hawaii • Mideast • Midwest • New England • Northwest • South Central • Southeast • Southwest • Virginia Area |
| Other | CPP • Geographic |
