Tag Archives: shadow
ArcGIS – CityEngine Urban Planning videos
For your viewing pleasure: 4 videos to accompany the CityEngine: Philadelphia example we published a couple of weeks ago. The videos show the full ArcGIS – CityEngine round trip:
- prepare your data in ArcGIS for input into CityEngine
- generate a 3D city in CityEngine from standard GIS data
- urban planning using CityEngine: design in 3D
- export your design and bring it back into ArcGIS for further and analysis and sharing
Note: you need to download the latest CityEngine Urban Planning Example for updated rules!
Have a good Xmas break and see you back in 2012!
Gert
Esri R&D Center Zürich
Shadow accuracy
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
New shadow templates available
We have made 2 new shadow templates available in our template gallery.
- 3D Virtual City: Shadows over time This template replaces the old shadow analysis template. It describes the process of creating volumetric shadows over time using the new Skyline Tools available in ArcGIS 10.
- Shadow Analysis: Shadow maps This template describes the process of analyzing volumetric shadows over time. The end result in this case is a so-called shadow map.
Enjoy!
Gert van Maren
3D Product Manager
Updated Shadow analysis template
Happy 2011!
The shadow analysis template on our resource center has been updated. We’ve improved the Sun Skymap tool which calculates the sun positions.
Improvements:
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the Sun Skymap tool works now in ArcScene as well as ArcGlobe
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automatically detects time zone based on machine time
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Horizonal elevation parameter (optional)
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Z factor parameter (optional)
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Tool help
The shadow analysis template shows you how to calculate volumetric shadows in ArcGIS10 using the Skyline tools.
Once you have calculated these shadow volumes, you can use them in subsequent analyses. For example you can calculate which windows receive shadow at a particular time.
In the screenshot below, the colored points represent window locations. Using the Inside3D tool, we can analyze which windows will receive sun (yellow), which windows will receive shadows from existing structures (blue) and which windows will receive shadows from the new proposed structure (red).
Along the same lines, we can calculate which facade areas will receive sun or shadow at any particular time. We can use Intersect3D to intersect the facade of a particular building of interest with the shadow volumes. This allows us to calculate the area affected by shadow of existing buildings, shadow of the proposed building or no shadow effect at all.
Please have a look at the GettingStarted_ShadowAnalysis.pdf in the template for more information on volumetric shadow analysis.
Gert van Maren
3D Product Manager
