Imagery Overlay

Imagery overlays supports JPEG 2000 (.jp2), ECW (.ecw), ECWP, MrSid (.sid), AGI's Processed Image format (.pdttx), and AGI's Roam Image format (.txm). The JPEG 2000, ECW, ECWP, and MrSid imagery must be in the WGS84 geographic projection. Generally, JPEG 2000 images take up less disk space than PDTTX images, but take slightly longer to load due to more sophisticated decompression.

Imagery is added in the same way as terrain as shown in the following example from the GraphicsHowTo application:

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//
              // Either jp2 or pdttx can be used here
              //
              IAgStkGraphicsGlobeImageOverlay overlay =
 scene.CentralBodies.Earth.Imagery.AddUriString(overlayPath);

Imagery is drawn on top of existing geometry, which may be the globe's ellipsoid or one or more terrain overlays as shown below.


Terrain and image overlays	Just image overlay

Translucency

Images can be blended with images below them by setting their translucency. This is controlled via the Translucency property. A translucency of 0% means the image is completely opaque, while a translucency of 100% means the image is completely transparent.

The following example sets an image's translucency to 40%.

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overlay.Translucency =
 0.4f;

Render Order

When images overlap each other on the globe, the central body's ImageCollection allows you to control which images are on top and which are below. The collection is ordered so the first image in the collection is rendered on the bottom; each subsequent image is rendered on top of the previous image if their extents overlap. The collection provides IndexOf, Swap and Move methods to order images as shown in the following example from the GraphicsHowTo application:

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IAgStkGraphicsGlobeImageOverlay
 topOverlay =
 scene.CentralBodies.Earth.Imagery.AddUriString(topOverlayPath);
                IAgStkGraphicsGlobeImageOverlay bottomOverlay =
 scene.CentralBodies.Earth.Imagery.AddUriString(bottomOverlayPath);

                //
                // Since bottom.jp2 was added after top.jp2, bottom.jp2 will be
                // drawn on top. In order to draw top.jp2 on top, we swap the
 Overlays.
                //
                scene.CentralBodies.Earth.Imagery.Swap(topOverlay,
 bottomOverlay);

Special Images

Imagery can have a special role, which can be either base, night or specular. These special images are drawn below all other imagery. A base image is normally used for a base globe texture. A night image is drawn only on the parts of the globe that aren't in sunlight. The specular image is drawn where the specular highlight is shown. This is typically used to dull the highlight on land areas to accentuate the shininess of the oceans.

The following example sets all three of the special images.

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IAgStkGraphicsSceneManager manager =
 ((IAgScenario)root.CurrentScenario).SceneManager;
                IAgStkGraphicsGlobeImageOverlay baseOverlay =
 manager.Initializers.GeospatialImageGlobeOverlay.InitializeWithString(baseOverlayPath) as IAgStkGraphicsGlobeImageOverlay;
                IAgStkGraphicsGlobeImageOverlay nightOverlay =
 manager.Initializers.GeospatialImageGlobeOverlay.InitializeWithString(nightOverlayPath) as IAgStkGraphicsGlobeImageOverlay;
                IAgStkGraphicsGlobeImageOverlay specularOverlay =
 manager.Initializers.GeospatialImageGlobeOverlay.InitializeWithString(specularOverlayPath) as IAgStkGraphicsGlobeImageOverlay;

                scene.CentralBodies.Earth.BaseOverlay = baseOverlay;
                scene.CentralBodies.Earth.NightOverlay = nightOverlay;
                scene.CentralBodies.Earth.SpecularOverlay = specularOverlay;


Just base image	Base and night images	Base and specular images

Imagery Cache

Since imagery files can be extremely large, the entire file is not kept in memory. Instead, a small portion of the file is kept in a memory cache. As the camera moves around, parts of the file are paged from disk into the cache. By default, the cache is 32 megabytes. If you are using high resolution imagery or the imagery appears blurry, try increasing the cache to 64 or 128 megabytes as shown below.

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IAgStkGraphicsSceneManager manager = ((IAgScenario)root.CurrentScenario).SceneManager;
				manager.GlobeOverlaySettings.ImageryCacheSize = 128;

Setting the cache above 128 megabytes is not recommended. Large cache sizes can slow down rendering since so much imagery will be rendered.