3 OVERLAY CONTROL CENTER

This section describes the Overlay Control Center dialog (pictured below). This dialog serves as the central control center handling all currently loaded data sets (overlays).


Currently Opened Overlays

This is a list of the all currently opened overlays. You can select an overlay by clicking on its name. Multiple overlays can be selected using the shift and control keys while clicking on overlays in the list. If the overlay is currently hidden, it is indicated to the left of the overlay description.

You can right click on the list of currently opened overlays to display a list of options available to perform on the selected overlays. Examples of available options include the following:

Create Elevation Grid from 3D Vector Data

Selecting the Create Elevation Grid from 3D Vector Data option on the popup menu that appears when right-clicking on vector layers in the Overlay Control Center displays the Elevation Grid Creation Options dialog, pictured below. Using this dialog, you can configure how you want the elevation grid to be created using the selected vector data as well as what portion of the selected overlays to use when creating the elevation grid. You can also use the Gridding tab to specify that your data should be gridded in sections. This makes it possible to grid data sets that are too large to grid all at once.


Metadata

Pressing the Metadata... button displays metadata for the selected overlay. The actual metadata dialog displayed depends on the type of the selected overlay. The metadata dialog for a SDTS DLG is shown below.


Options

Pressing the Options... button displays a dialog containing the available display options for the selected overlay(s). Options can be set on multiple raster or elevation overlays at the same time. The available display options depend on the type of the selected overlays. The following display options are used:

Shapefile Data Options

Selecting the Options... button while an ESRI Shapefile overlay is selected displays the Shapefile Options dialog (pictured below).


The Feature Types tab provides the ability to specify which attribute field (if any) to display as the name of features loaded from the Shapefile. You can also specify the feature type to assign to features loaded from the Shapefile.

The Projection tab is used to reinterpret the raw vector data to a new projection. This is useful if the wrong projection was selected for the dataset when it was loaded, or if the data set itself indicated some incorrect data. This option is rarely used.

Vector Data Options

Selecting the Options... button while a vector (i.e. DLG, DXF, E00, etc) overlay is selected displays the Vector Options dialog (pictured below). This dialog is used to reinterpret the raw vector data to a new projection. This is useful if the wrong projection was selected for the dataset when it was loaded, or if the data set itself indicated some incorrect data. This option is rarely used. You can however also use the Elevation Units control to specify what elevation units that values in the vector data that do not explicitly specify their units should use. This is useful to indicate if the values associated with 3D vector features or with the ELEVATION attribute for features are in feet or meters.


For many vector formats, you will also see a Feature Types tab (pictured below), which will allow you to select what Global Mapper classification to assign to the unclassified area, line, and point features in the layer.


Raster Data Options

Selecting the Options... button while only raster overlays are selected displays the Raster Options dialog. The Raster Options dialog consists of several tabs, each allowing you to control various aspects of how the selected raster layers are displayed.

The Display tab (pictured below) contains controls allowing you to control the color intensity (brightness/darkness), color transparency, blending, anti-aliasing, and texture mapping of the selected layers.


The Color Intensity setting controls whether displayed pixels are lightened or darkened before being displayed. It may be useful to lighten or darken raster overlays in order to see overlaying vector data clearly.

The Translucency setting controls to what degree you can see through the overlay to overlays underneath the overlay. The default setting of Opaque means that you cannot see through the overlay at all. Settings closer to Transparent make the overlay increasingly more see-through, allowing you to blend overlapping data.

The Blend Mode setting controls how an overlay is blended with underlying overlays, in addition to the Translucency setting. These settings allow Photoshop-style filters to be applied to overlays, resulting in often stunning results. What you get from a particular set of overlays from a particular blend mode setting can often be hard to predict, so rather than try to understand what is technically happening for each blend mode it's best to just experiment with different ones until you find one that you like. The Hard Light setting seems to work well with satellite imagery overlaid on DEMs, but the others can be quite useful as well. For example, the Apply Color setting is useful for applying color to a grayscale overlay, such as using a low-resolution color LANDSAT image to colorize a high-resolution grayscale satellite image.

The Transparent option allows a particular color to be displayed transparently, making it possible to see through a layer to the layers underneath. For example, when viewing a DRG on top of a DOQ, making the white in the DRG transparent makes it possible to see much of the DOQ underneath. Pressing the Set Transparent Color... button allows the user to select the color to treat as transparent in the selected overlay(s).

The Anti-Alias Pixels (Interpolate) option removes jagged edges by making a subtle transition between pixels. Turning off this option helps maintain the hard edges of the pixels as they are rasterized.

The Texture Map option allows a 2D raster overlay to be draped over loaded 3D elevation overlays. Selecting the check box causes the overlay to use any available data from underlying elevation layers to determine how to color the DRG or DOQ. The result is a shaded relief map.

The Color/Contrast Adjustment tab (pictured below) allows you to control the color balance and contrast of the selected overlay(s).


The Color Balance sliders allow you modify the relative amounts of red, green, and blue in the image, thus allowing precise control over the color balance in the image.

The Contrast Adjustment options are used to adjust the contrast of imagery. The Linear (Percentage Stretch) contrast adjustment method applies a standard deviation contrast adjust to each color channel in the image. You can specify how many standard deviations from the mean that the range is stretch to for rendering, although you'll generally want to stick with the default of 2. This is particularly useful for improving the display of dark or satellite imagery, such as IKONOS images, and is required for the display of imagery with more than 8 bits per color channe. The Linear (Min/Max Stretch) method finds the minimum and maximum values in each color channel and stretches that range to a range of 0 to 255. For most imagery with 8 bits or less per color channel this will have no effect, but can produce a good result for high-color imagery.

The Cropping tab (pictured below) allows you to crop the selected overlay(s) to a particular boundary, including support for automatically removing the collars from USGS DRG topographic maps.


The Automatically Crop DRG-style Collar option is used to automatically remove the collar from loaded raster data. Most frequently it is used to removes the white border around a DRG or the small black collar around a 3.75 minute DOQQ. This allows you to seamlessly view a collection of adjacent DRG or DOQQ files.

The Crop to Manually Specified Lat/Lon Boundary option allows you to specify a lat/lon boundary (in the native datum of the selected overlay) to crop the overlay to. When selected, this option will display the Customize Collar Bounds dialog (pictured below) to allow specifying the bounds to crop to.


The Crop to Manually Specified Boundary in Native Layer Projection/Units option allows you to specify a crop boundary in the native units of the selected overlay. When selected, this option will display the Customize Collar Bounds dialog (pictured above) to allow specifying the bounds to crop to.

The Crop a Specified Number of Pixels Around the Edges of the Layer option allows you to specify a number of pixels to crop of each edge of the selected overlay(s).

The Feathering tab (pictured below) allows you specify that you would like to feather-blend the selected overlay(s) with the underlying overlay(s) on the specified edges. This can be extremely powerful tool for blending imagery/maps from different sources and/or at different resolution to make the edge between the map sets invisible.


The screenshot below displays the results of feather-blending a very high resolution data set (0.15 meters per pixel) with a lower resolution (3.5 meters per pixel) dataset to remove the edge. Note that the higher resolution image has been purposely tinted violet to make the effect more obvious.


Elevation Data Options

Selecting the Options... button while only gridded elevation overlays are selected displays the Elevation Options dialog. The Elevation Options dialog consists of two tabs, one for controlling the display of the overlay(s) and the other for modifying the elevation values within the overlay(s).

The Display tab (pictured below) contains controls allowing you to control the color intensity (brightness/darkness), color transparency, blending, anti-aliasing, and color shading of the selected layers.


The Color Intensity setting controls whether displayed pixels are lightened or darkened before being displayed. It may be useful to lighten or darken raster overlays in order to see overlaying vector data clearly.

The Translucency setting controls to what degree you can see through the overlay to overlays underneat the overlay. The default setting of Opaque means that you cannot see through the overlay at all. Settings closer to Transparent make the overlay increasingly more see-through, allowing you to blend overlapping data.

The Blend Mode setting controls how an overlay is blended with underlying overlays, in addition to the Translucency setting. These settings allow Photoshop-style filters to be applied to overlays, resulting in often stunning results. What you get from a particular set of overlays from a particular blend mode setting can often be hard to predict, so rather than try to understand what is technically happening for each blend mode it's best to just experiment with different ones until you find one that you like. The Hard Light setting seems to work well with satellite imagery overlaid on DEMs, but the others can be quite useful as well.

The Transparent option allows a particular color to be displayed transparently, making it possible to see through a layer to the layers underneath. For example, when viewing a DRG on top of a DOQ, making the white in the DRG transparent makes it possible to see much of the DOQ underneath. Pressing the Set Transparent Color... button allows the user to select the color to treat as transparent in the selected overlay.

The Anti-Alias Pixels (Interpolate) option removes jagged edges by making a subtle transition between pixels. Turning off this option helps maintain the hard edges of the pixels as they are rasterized.

The Shader option allows you to choose which elevation shader is to be used for coloring the cell values within this layer. By default, all gridded layers will share the elevation shader selected on the toolbar, but there may be certain situations where you want to color one layer differently than the others and exclude it from the loaded elevation range. One common example is a gridded layer that actually has non-elevation data.

The Alter Elevation Values tab (pictured below) allows you to modify how elevation values from the selected layer(s) are interpreted, providing you a means to offset all of the elevations in the layer(s) by a given value and to restrict the range of elevation values that are treated as valid.


Show/Hide Overlay(s)

Toggles whether the currently selected overlays are visible.

Close Overlay(s)

Closes all the currently selected overlays.