Utilities SDK

The osgEarth Utils namespace includes a variety of useful classes for interacting with the map. None of these are strictly necessary for using osgEarth, but they do make it easier to perform some common operations.

Logarithmic Depth Buffer

In whole-earth applications it’s common that you want to see something up close (like an aircraft at altitude) while seeing the Earth and its horizon off in the distance. This poses a problem for modern graphic hardware because the standard depth buffer precision heavily favors objects closer to the camera, and viewing such a wide range of objects leads to “z-fighting” artifacts.

The LogarithmicDepthBuffer is one way to solve this problem. It uses a shader to re-map the GPU’s depth buffer values so they can be put to better use in this type of scenario.

It’s easy to install:

LogarithmicDepthBuffer logdepth;
logdepth->install( view->getCamera() );

Or you can activate it from osgearth_viewer or other examples:

osgearth_viewer --logdepth ...

Since it does alter the projection-space coordinates of your geometry at draw time, you do need to be careful that you aren’t doing anything ELSE in clip space in your own custom shaders that would conflict with this.

(10-Jul-2014: Some osgEarth features are incompatible with the log depth buffer; namely, GPU clamping and Shadowing. Depth Offset works correctly though.)

Formatters

Use Formatters to format geospatial coordinates as a string. There are two stock formatters, the LatLongFormatter and the MGRSFormatter. A formatter takes a GeoPoint and returns a std::string like so:

LatLongFormatter formatter;
GeoPoint point;
....
std::string = formatter.format( point );

LatLongFormatter

The LatLongFormatter takes coordinates and generates a string. It supports the following formats:

FORMAT_DECIMAL_DEGREES:  34.04582 FORMAT_DEGREES_DECIMAL_MINUTES:  34.20:30 FORMAT_DEGREES_MINUTES_SECONDS:  34:14:30

You can also specify options for the output string:

USE_SYMBOLS:Use the degrees, minutes and seconds symbology USE_COLONS:Use colons between the components USE_SPACES:Use spaces between the components

MGRSFormatter

The MGRSFormatter constructs a string according to the Military Grid Reference System. Technically, an MGRS coordinate represents a region rather than an exact point, so you have to specify a precision qualifier to control the size of the represented region. Example:

MGRSFormatter mgrs( MGRFormatter::PRECISION_1000M );
std::string str = mgrs.format( geopoint );

MouseCoordsTool

The MouseCoordsTool reports the map coordinates under the mouse (or other pointing device). Install a callback to respond to the reports. MouseCoordsTool is an osgGA::GUIEventHandler that you can install on a Viewer or any Node, like so:

MouseCoordsTool* tool = new MouseCoordsTool();
tool->addCallback( new MyCallback() );
viewer.addEventHandler( tool );

Create your own callback to respond to reports. Here is an example that prints the X,Y under the mouse to a Qt status bar:

struct PrintCoordsToStatusBar : public MouseCoordsTool::Callback
{
public:
    PrintCoordsToStatusBar(QStatusBar* sb) : _sb(sb) { }

    void set(const GeoPoint& p, osg::View* view, MapNode* mapNode)
    {
        std::string str = osgEarth::Stringify() << p.y() << ", " << p.x();
        _sb->showMessage( QString(str.c_str()) );
    }

    void reset(osg::View* view, MapNode* mapNode)
    {
        _sb->showMessage( QString("out of range") );
    }

    QStatusBar* _sb;
};

For your convenience, MouseCoordsTool also comes with a stock callback that will print the coords to osgEarthUtil::Controls::LabelControl. You can even pass a LabelControl to the constructor to make it even easier.