5.3 3D Visualization & Scenes

Global vs. Local Scenes

ArcGIS Pro maps can be converted into 3D environments called Scenes. There are two primary types of scenes, and choosing the correct one is vital for your project:

1. Global Scene: Used for large-scale, earth-wide visualizations. It displays the earth as a globe using a geographic coordinate system (typically WGS 1984). It is ideal for visual phenomena that span continents, global weather patterns, or airline flight paths.
2. Local Scene: Used for smaller, localized extents. It displays the earth on a flat, projected surface (like a State Plane or UTM coordinate system). It is best for city planning, localized site analysis, or viewing subsurface data (like well bores or underground utilities), as it allows for clipping the extent to a specific study area.

Elevation Surfaces

In a scene, 2D layers are 'draped' over an elevation surface. By default, ArcGIS Pro includes the World Elevation Service. You can add your own DEM (Digital Elevation Model), TIN, or LAS datasets as elevation sources to provide higher resolution terrain for your study area.

Layers can be configured to draw:

• On the ground: Draped directly over the elevation surface.
• Relative to the ground: Features are lifted above the surface by a specific attribute or constant value (e.g., an airplane flight path offset by its altitude attribute plus the ground elevation).
• At an absolute height: Features ignore the ground surface and use their own Z-values or an attribute to determine height above sea level.

Extrusion and 3D Symbology

Extrusion is the process of stretching a flat 2D shape vertically to create a 3D object. The extrusion height is usually driven by an attribute, such as the HEIGHT or FLOORS field of a building footprint layer.

Types of Extrusion:

• Min/Max Height: Extrudes from the minimum or maximum Z-value of the geometry.
• Base Height: Extrudes upward from the base of the feature.
• Absolute Height: Extrudes to a specific absolute elevation.

For more realistic visualization, you can use 3D symbols (multipatch features) or Procedural Symbology. Procedural symbols use CityEngine rules (.cga) to dynamically generate complex 3D structures, like textured buildings with windows and roofs, based on 2D footprints and attributes.

Detailed Scene Authoring and Performance

To master 3D visualization for the exam, you must deeply understand the implications of Z-values. A feature class can be Z-enabled (meaning it stores a Z-coordinate for every vertex) or Z-disabled. In a scene, Z-enabled features can inherently draw at their absolute heights using their geometry. Z-disabled features must rely on attributes or the ground surface for their vertical placement.

When working with subsurface data (like geologic strata or underground pipes), a Local Scene is strictly required. Global scenes do not support navigating below the ground surface effectively, and they enforce the curvature of the earth. In a Local Scene, you can set the ground surface to have a negative transparency or clip it to a specific extent, allowing the camera to pan underground and inspect subsurface infrastructure. This is a common exam scenario: choosing between Local and Global based on the need for subsurface viewing.

Another critical topic is the integration of BIM (Building Information Modeling) and CAD data. ArcGIS Pro natively reads Revit (.rvt) and IFC files. When these are added to a Scene, they appear as complex 3D objects with hierarchical structures (e.g., Walls, Roofs, Doors). You can use the slice tool or building filter tools to interactively explore the interior of these models. Knowing that BIM data is best viewed in a Local Scene due to its projected coordinate system requirements is important.

Voxel layers are a newer addition to ArcGIS Pro's 3D capabilities. Voxel layers represent multi-dimensional volumetric data, such as atmospheric pollution plumes or subsurface ocean temperatures over time. They are inherently 3D (and often 4D with time) and are rendered using a specialized voxel engine. You can slice voxels, create isosurfaces (surfaces of equal value), and filter by values to visualize complex scientific data.

Performance in 3D scenes relies heavily on the graphics hardware (GPU). To optimize scenes:

• Use Scene Cache: Publishing 3D layers as Web Scene Layers generates a highly optimized i3s cache (Indexed 3D Scene). This is crucial for sharing 3D content to the web.
• Simplify geometry: Just as in 2D, overly complex 3D models hurt performance. Use generalization or simplify 3D models if high detail is not required.
• Distance visibility: Set visibility ranges for 3D layers so high-detail multipatch buildings only draw when zoomed in closely, falling back to simple extruded polygons or 2D footprints when zoomed out.

Lighting and atmospheric effects also play a role in 3D cartography. In the Scene properties, you can configure the illumination based on a specific date, time, and time zone. This allows for realistic shadow analysis, such as determining if a proposed high-rise building will cast a shadow over a park during winter afternoons. You can also enable atmospheric effects like stars, atmospheric scattering, and fog to enhance realism.

Remember the workflow for extruding a polygon: Select the layer, go to the Appearance tab (under Feature Layer), find the Extrusion group, select the Type (e.g., Base Height), and specify the Field or Expression. This UI path is fair game for the exam. Furthermore, if extrusion is not available on the ribbon, it is usually because the layer is in a 2D map instead of a 3D scene, or the layer is not a polygon/point/line feature class (e.g., you cannot extrude a raster).

Finally, understand the Animation framework in ArcGIS Pro. You can create compelling 3D fly-throughs by capturing keyframes. The animation interpolates the camera path between these keyframes. You can also animate layer visibility, time, and range properties, exporting the final result to standard video formats (MP4, AVI). This is an advanced visualization technique often tested in the context of presenting results to stakeholders.