On Friday, July 17th, many ArcGIS Pro users saw a small window pop up on their computer screen. It announced to them, and to the world that a new version of Pro is available to download. I often find myself … Continue reading
A number of users have commented on occasional differences between computed shadow volumes and observed shadows.
There are a couple of possibilities that could account for the differences observed in the shadow model output and the real world shadow.
Please consider the following:
- Data discrepancy between your building model and the actual building, or your surface model and the actual surface. Coarse resolution elevation data can introduce a significant variation from the observed proof points.
Make sure your building models represent the actual buildings and increase the resolution of your terrain data when comparing shadows. In ArcScene: Layer properties -> Base Heights -> Raster Surface Resolution.
- Data offset of Sun point feature caused by the transformation of the Sun’s position to the spatial reference of the input feature class. The Sun point is initially calculated in GCS WGS 1984, then projected into the spatial reference of the input feature. If the datum of the input feature is different than WGS 1984, then a default transformation is applied. This would typically be the first available option unless a particular transformation is specified in the environment setting. An improper datum transformation can result in an offset of up to 30 feet, depending on the locale and the method being used.
Please check the spatial reference of your input building feature and see if it necessitates the specification of a datum transformation. This help article offers a guide for determining the appropriate transformation.
Also the impact of such an offset on the final shadow output is reduced if the output Sun distance is increased. For example increase the distance from default 2500 to 10000.
- Our tools use a point source, whereas the shadow measured out in the field is generated by a sun which has a significant angular diameter (0.5 degrees): soft vs hard shadows.
- Another factor might be refraction, which is not considered in the create SunSkyMap script. Refraction causes the sun to appear higher than the theoretical position value, meaning that the shadow will be calculated shorter.
Gert van Maren
3D Product Manager
Some users have noticed that the option to display lines using 3D Simple Line symbols – tubes, strips and walls – is not available in ArcGlobe. This is a current technical limitation with ArcGlobe’s rendering pipeline (which has not been addressed in 10 or 10.1).
So, if you need them, how do you display tubes in ArcGlobe? The answer is to generate multipatch features from the displayed geometry in ArcScene.
The process is fairly simple:
Symbolize your line data in ArcScene as tubes (using a 3D Simple Line Symbol)
- Use the Layer 3D to Feature Class GP tool to create a new multipatch feature class from the symbolized layer.
- Then display the multipatch data in ArcGlobe
Things to be aware of:
Do not ratchet up the tube ‘Quality’ slider when you define the layer – this will minimize the number of triangles to be displayed later
Generate a full data cache for that layer in ArcGlobe (available on the layer’s context menu in the TOC
Aggressively use the distance-based visibility setting so you don’t see too many tubes at once
The layer will work marginally better as “floating” (ie: has absolute z-values embedded) than as “draped”
For those unfamiliar with multipatch features, it is simply a geometry type (like points, lines and polygons) where the geometry is captured in 3D triangles. Like all other geometry types, it supports database concepts such as attribute fields, subtypes, relationship classes and table joins. Multipatch layers can also use the various rendering options, such as attribute-driven colors, distance-based visibility, HTML popups, etc.
It’s also worth mentioning that the most current release of ArcGIS 3D Analyst (soon to be 10.0 SP2) contains a significant amount of performance improvements for displaying multipatches.