GIS Conversion and Editing

Example of a GIS item right-click menu in SMS.

GMS, SMS, and WMS can load GIS data such as digital elevation models (DEMs) and images. This GIS data will appear in the GIS Data section of the project explorer.

GIS Data Conversion

Both GMS and SMS offer methods to convert GIS data. Right-clicking on a GIS data item in the project explorer brings up a menu with a Convert To sub-menu. The commands in the Convert To sub-menu are:

Raster to 2D Scatter

Selecting the command Convert To | 2D Scatter will bring up the Raster → Scatter dialog. The dialog shows the number of scatter point that will be generated in the new set and lets the user name the new scatter set. By default, the name of new scatter set will be the same as the raster set unless changed.

Example of the Raster → Scatter dialog.

By default scatter points are shown in red unless changed in the Display Options dialog. Users may need to zoom in to see each point. Scatter points are visible in other views while the DEM is visible only in plan view.

Example of a scatter set generated from a raster set.

Feature Contours

Activating this command will automatically generate contours which will appear as a new coverage under Map Data in the project explorer. By default, contour lines are shown in black unless the user changes the contour color in the Display Options dialog. The contour interval is found by creating 10 contours evenly spaced between the min and max dataset values.

Generated feature contours appearing as black lines.

Feature Contours at Given Elevation

Example of the Create Contour Arc dialog.

This command will bring up the Create Contour Arc dialog. In this dialog the user can specify an elevation to be used in generating the contours.

After entering an elevation and clicking OK, contours will be generated similar to those created with the Feature Contours command but using the specified elevation. Only contours at the specified elevation will be generated.

Example of feature contours generated using a given elevation.

GIS Data Editing

Resampled Raster

Resample and Export Raster dialog.

This command will bring up the Resample and Export Raster dialog. The dialog has the following options:

• Cell size – specify the size of each cell based on the Resampling ratio.
• Resampling ratio – specifies the resampling ratio. This is required for processing. Changing this field will change the other fields in the dialog automatically.
• Num pixels X – the number of pixels on the x axis that will be generated. The original number will be displayed to the right.
• Num pixels Y – the number of pixels on the y axis. The original number will be displayed to the right.
• Add to project after saving – toggling this option on will load the resampled file into GMS/SMS upon completion.

After completing the Resample and Export Raster dialog and clicking OK the Save As dialog will appear allowing the user to save a file with the resampled data.

Example of resampled raster data.

Smoothed Raster

Raster Smoothing Options dialog.

This command will bring up the Raster Smoothing Options dialog. The dialog has the following options:

• Filter Size – to smooth the raster, an N x N filter matrix is placed over each elevation point and a new elevation is computed by taking an inverse-distance weighted average of all elevations within the filter. The dimension of N can be specified as either 3x3 or 5x5, meaning that new elevations are computed from either the nearest 8 or 24 neighboring points.
• Number of iterations – specify the number of smoothing iterations. By default only one iteration is done, but sometimes several smoothing iterations are required to propagate a change in elevations across a large flat area.
• Maximum change in elevation – can be used to ensure that the integrity of the original elevations are maintained.
• Filter ratio – should be between 0-1, and is used to specify the weight of the central cell of the filtering matrix.

After completing th Raster Smoothing Options dialog and clicking OK the Save As dialog will appear allowing the user to save a file with the smoothed data.

Trimmed Raster

Coverage polygons must be selected to define the trimming rectangle. If this is not done, then a warning dialog will appear as a reminder.

To create a trimmed raster:

1. Select a coverage (or create a new coverage) in the Map module.
2. Select the Create Arc tool and draw a closed set of arcs.

   

   Closed set of arcs drawn over a raster.

3. While the arcs are selected, go to Feature Objects |Build Polygons.
4. Use the Select Polygon tool to select the polygon just created.

   

   Selected polygon just prior to using the Trimmed Raster command.

5. Right-click a DEM in the GIS data and select Convert To | Trimmed Raster.
6. The Save As dialog will appear allowing the user to save a file with the trimmed data.

   

   Example of a trimmed raster.

The final raster is trimmed along the rectangle enclosing the polygon. Trimmed rasters will also trim to the rectangle enclosing multiple selected polygons.

Merged Raster

Two or more DEM datasets can be merged together by doing the following:

1. Select two or more DEM items in the project explorer by holding down the Shift key while selecting each item.
2. Right-click on one of the selected DEMs and select Convert To | Merged Raster. This command is only available when multiple raster items have been selected.
3. The Save As dialog will appear to save a file with the merged data.

The new merged DEM will be visible in the project explorer. When merging, the smallest cell size among the merging rasters is used.

Saving Raster Data

Raster data being converted can be save in any of the following formats:

GeoTiff Files (*.tif) BIL Files (*.bil) Erdas Imagine IMG Files (*.img) Surfer ASCII Grid Files (*.grd) Surfer Binary grid v6 Files (*.grd) Surfer Binary Grid v7 Files (*.grd) USGS ASCII DEM Files (*.dem) XYZ ASCII Grid Files (*.xyz)

Arc Info ASCII Grid Files (*.asc) DXF 3D Point Files (*.dxf) Float/Grid Files (*.flt) DTED Files (*.dtf) Vertical Mapper (MapInfo) Grid Files (*.grd) Global Mapper Grid Files (*.gmp) Windsim GWS Files (*.gws)

Related Topics

Raster Options Smoothing DEMs

GMS GIS Module SMS GIS Module