Understanding Design Regulation in 3D

So far in these tutorials we have looked at data that is two-dimensional. Polygons or Picxels (cells) with attributes. Sometimes these attributes might be considered as a third dimension, especially when the denote the height of something, like a building polygon, or a cell in a digital elevation model. IN this tutorial we are going to explore how this psuedo-3D data can be visualized. These visualizations can be useful for getting an idea of how places look from the ground or a bird's-eye perspective. More intersting is how these tools can help us visualize how places might look under various design or regulatory scenarios.

The Tools

The tools we will look at in this tutorial are ArcGIS and ArcGlobe. ArcMap was used for transforming the datasets, and we will use ArcMap to create and edit information. ArcGlobe is the tool that portrays data in three dimensions and permits us to move around the scene to capture images and animations. The following software manuals will be indispensible for understanding the procedures coverdd in this tutorial:

• Using ArcGIS 3D Analyst
• Editing in ArcMap
• Notes on Making Animations and Troubleshooting Problems with ArcGlobe
• Notes on Making Animations and Troubleshooting Problems with ArcGlobe
• About Using Lookup Tables in ArcMap
• About Clipping Areas out of the Boston Metropolitan 3d Model

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Right-Click to Download the Sample Dataset

This lab is a work in progress. We will discuss the following topics in the lab:

1. An examination of the data: Zoning, Raster Elevation Model,
2. About Lookup Tables
3. Using the Development Potential Calculator
4. Editing Attributes
5. Editing Geometry
6. Composing 3d scenes in arcglobe

The Data

The database for this project comes form several sources. We have transformed it slightly and arranged it as a schema in arcgis using a personal geodatabase, which is a way of using a microsoft access database to store spatial data and relationships. You can use windows explorer to examine the files in the folder somerville_3d\orig_scenario. You can use ArcCatalog to check out the datasets and their properties. Make sure to click all the way into the geodatase to see the three feature classes inside there. Make sure to close ArcCatalog before opening the data in ArcMap. When you examine the properties in a geodatabse in ArcCatalog it locks the scehma so that someone else can't alter the data.You can then open up the ArcMap document ArcMap.mxd to view the datasets and their attribute table.

The Zoning Dimensional Standards Lookup Table

Be sure to change your Table of Contents view to Source using the tabs at the bottom so that you can open the table zonecode_lut. This is a lookup table that provides the dimensional standards for each of the zoning classes in the Somerville Zoning Ordinance.

The Buildings Layer

The buildings layer has a polygon for each building. YOu can see that each polygon has a height attribute. This data comes form MassGIS, who did a laser scan LIDAR of the entire core boston region.

The Potential_Parcels Layer

This layer has been made by intersecting a layer of somerville right-of-way polygons with the layer of somerville zoning districts. This has resulted in a new polygon layer that has assigned to each block the attributes of its zoning district. Wherever the boundary of a zonig district cuts through a block, the block polygon is divided. Even though we know that in reality, each of these areas is further subdivided by property parcels, but since our model is about understanding Development Potential we will assume that a developer couls buy and aggregate parcels, and thus the development potential of each block is strictly a function of the dimensional restrictions as given in the zoning ordinance.

The Zoning Layer is Joined with the Zonecode Lookup Table

The zoning layer is made up of a feature dataset that has been made from the somerville zoning data layer. We have used an Intersect function to cut it with a data layer of the Somerville blocks. This has allowed us to put the streets into their own zone, Rights of Way or RoW, and has fragmented the large zonign polygons into separate polygons for each block. If you take a look at the attribute table of this layer, you will see that each attribute name has a prefix denoting that some of the attributes are from the Zoning feature class, and some are from the zonecode_lut table. This is accomplished with a Relational Join. You can learn more about joins by looking this concept up in the ArcMap user Guide.

Understanding this join is critical for learning how to adjust the dimensional standards for zones. The marvel of this is that the Lookup Table is the master source for information about the relationship between zonecodes and dimensional attributes. The Zoning Table carries information about the zonecodes for each polygon. If you want to change the dimensional standard for a zonecode, you make this change in the lookup table. The join will update the changed information for each polygon in that zone automatically. To observe this, you can do the following experiment:

Changing the Geometry and Attributes of Potential Parcels

Ou can use the ArcGIS editing tools to modify the geometry of developable parcels. Tips on editing in arcMap can be vound in the ArcGIS User GuideEditng in ArcMap, for tips on modifying geometry of shape files. Note that since the Potential Parcels Layer is a geodatabase feature class, the Shape Area column updates itself automatically! The units here are Feet.

Adding a New Zoning Classes

Note that I have added a couple of new Special Zoning District classes to the bottom of the ZoneCode Lookup Table these special districts are not part of the existing zoning ordinance, but you can use them to experiment with creating special zones. YOu can define the dimensional requirments for a specific area, and then you can assign the Code attribute to any parcel you select or create, to assign the new development potential to any area of the map that you want.

Calculating the Development Potential of Each Developable Parcel

Note that each developable area has an attribute called Dev_Area. This attribute holds the number of square feet of development that a Potential_Parcel can support. This is not the two-dimensional area of the polygon, but a function of the parcel area, the percent of the lot that can be built on, and the Floor Area Ratio. (the two latter attributes are from the Zonecode Lookup Table. To translate this function into the attribute names in our schema, we would say:

Dev_Area = Shape_Area * FAR * Ft_Area_r

If we change the dimensional standards for a zone in the Lookup Table or if we change the size of any developable parcel we must recalculate the the developable area for each of the developable parcels. You can do this with the Field->Calculate Values wizard from the Data Management toolbox. For more information on how to use this tool, click the Show Help button at the bottom of the wizard. See Picture.

Calculating Total Potential Development Area

Our problem is that we want to accomadate a certain amount of new development in different areas of the city by creating new special transit oriented zoning districts. Once we do this we aant to calculate the total amount of development in each district or in particular areas of the city.

Tabulating the total developable area for each zoning district can be done with the Analysis->Statistics->Summary Statistics tool from the toolbox. You can read more about how this tool works by clicking the Show Help button on this wizard. The result of this calculation will be a new table, added to our table of contents showing the amount of square feet of developable floor area in each district. This table can be saved in the geodatabase, or as a database file (.dbf) that can be opened in excel. Note that ArcMap will not display a table if it is opened in another application.

If we have a subset of potential parcels selected, the Summary Statistics tool tabulates statistics for just those parcels. It is very useful to create a virtual layer representing a subset of your parcels by making a selection from the layer, the right clicking on it and choosing Selection->Create Layer from Selected Features. It is critical to understand that layer files created this way are Views of the original layer. They are not independent datasets. They reflect changes made on the parent layer and vice-versa. This is very useful, since you can continue to use the Potential_parcels layer to make changes anywhere in the city, and any selection layers that you make will automatically be updated.

Visualizing Your Sceneario in 3D!

Opening the file, ArcGlobe.3dd will provide a view of your results in 3D! Be sure to right-click on all of your layers and choose Refresh to make sure that your changes are reflected. This may even be necessary to refresh layers the first time you start ArcGlobe since it creates a 3d cache.

References

• Somerville Zoning Dimensional Requirements