Esri and the 3rd dimension

With Esri’s ever expanding software stack it is sometimes difficult to keep track of the variety of software solutions available. One of the main areas of growth is Esri’s collection is its answer to 3D GIS. Fully utilising the extra dimension has come difficult to the GIS sector in the past (which is historically mostly two-dimensional in terms of application). Esri’s recent focus on developing a 3D stack which fully embraces three-dimensional analysis, content generation and visualisation with the emphasis on sharing 3D scenes with non-technical users has led to mainly two desktop applications, ArcGIS Pro and CityEngine. This blog post will have a look at both of these applications by discussing the capabilities and when to use them through a typical use-case for an area around central Johannesburg.

Intro
CityEngine or ArcGIS Pro

ArcGIS Pro:

ArcGISPro

ArcGIS Pro allows users to seamlessly integrate traditional two-dimensional GIS with 3D data in a single application interface. Using the 3D Analyst extension a user can perform various 3D analysis on GIS data including line of sight, volumetric calculations, viewshed calculations as well as working with LAS datasets, as well as the traditional GIS analysis methods like proximity, overlay and statistical analysis. For more information regarding the 3D Analyst extension visit: http://www.esri.com/software/arcgis/extensions/3danalyst.

The image below shows a Johannesburg scene showing 3D textured buildings, analytical representation of trees and extruded polygons showing the various zones and height restrictions of the buildings. This gives the user the ability to quickly see which building exceed their height restrictions.

ArcGISPro001
Overlay 3D buildings and zonal restrictions in ArcGIS Pro

Next we need to calculate how the shadows in the city change over course of a specific day, and share the result with external users.

Use the Sun Shadow Volume geoprocessing tool (3D Analyst) to calculate the shadow volumes. In the example below the analysis were done between 08:00 and 16:00 for every two hours.

ArcGISPro002
Sun shadow volume tool

The resulting multipatch represents the shadow volumes created by each building at a specific time. ArcGIS Pro has the ability to cycle through these time-enabled data to create a seamless animation of the shadow movement.

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Shadow movement over the course of the day

Share the scene to either ArcGIS Online or Portal with ease. An example web scene for of the shadow analysis mentioned above can be viewed here.

*The next blog post will focus on the various 3D sharing techniques available in the ArcGIS Platform

ArcGIS Pro is a powerful tool for performing 3 dimensional analysis on GIS data. However, although ArcGIS Pro has 3D editing capabilities, its primary function is not 3D content creation. CityEngine on the other hand was designed especially for quick content generation on a large scale.

CityEngine:

CE

CityEngine’s ability to dynamically create and compare urban scenarios quickly makes it a favourite among urban developers, local governmental authorities, township planners as well as the entertainment industry.

The key behind CityEngine’s quick content generation is its own procedural scripting language called CGA. These scripts or rules are basically a set of sequential tasks that guides the software to create accurate 3D geometries.

By applying different rules to the same datasets, we are able to generate various 3D representations. In the example below, we can see that in the larger view a more realistic scenario is generated displaying textured buildings and highly detailed trees. The inserted image shows the same datasets represented differently to produce a more analytical scenario of the data.

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Using CGA rules creates multiple scenarios quickly using the same data

In another example, an urban designer might want to compare scenarios for a redevelopment project. In the image below CityEngine is used to compare high rising buildings, office spaces and apartment building designs.

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Comparing redevelopment strategies in CityEngine

A CityEninge scene can be easily shared in a variety of ways. These include:

A CityEngine webscene is a static version of the CityEngine scene. All models, terrains and networks generated in CityEngine is compressed into a single .3ws file. This file can then be added as an item in ArcGIS Online or Portal, and when opened creates a browser based 3D environment that allows user-driven navigation and interaction. An example of the CityEngine web scene can be found here.

The image above shows examples of:

  • comparing real-world and analytical scenes (top left)
  • comparing redevelopment scenarios (top right)
  • adding HTML embedded attributes such as Google Streetview (bottom)

Datasets can also be exported to a Scene layer package. A Scene layer package has the ability to publish hosted scene layers which represents 3D data as a feature service, when added to either ArcGIS Online or Portal.

CityEngine also has the ability to share a scene as a 360 Virtual Reality experience. This creates a .3vr file which can be shared to ArcGIS online. Using a Samsung Gear VR headset along with the ArcGIS 360 VR app from Esri Labs, you are able to explore scenes in a fully immersive 3D virtual reality.

Find the Johannesburg 360 virtual reality scene here.

VR

For more information about creating a 360 VR experience in CityEngine go to the Esri CityEngine Help.

Projection, Georeferencing and Spatial Adjustment CAD

Projection

A map projection is a method for taking the curved surface of the Earth (3D) and displaying it on a flat surface (2D). A projected coordinate system is always based on a geographic coordinate system. The below table shows a few key differences between a GCS and PCS.

GCS (Geographic Coordinate System) PCS (Projected Coordinate System)
3D Spheroid Surface 2D Flat Surface
Latitude and Longitude XY Locations
Datum Map Projection

Map projections are designed for specific purposes. Conformal projections preserve the shape of the features, Equal area projections preserve the area of the feature displayed, Equidistant projections preserve the distance between certain features on a map while the Azimuthal projection maintains the directions of all points on the map.

Common Errors Due to Incorrectly set Coordinate Systems

 

Quick Easy Steps for Projecting

  1. Enquire with the source owner of the data, research or decide which coordinate system the data should be assigned. If the original coordinate system of the data cannot be sourced, it will be your responsibility to assign the correct coordinate system to the data.
  2. Before deciding which coordinate system the data should be assigned; visually assess the data or the layer properties of the data, to check whether the data is originally in GCS (Geographic Coordinate System) or PCS (Projected Coordinate System). Add the data in the Map Window in ArcMap.
    extent
    Take note of the Extent that has large numbers 361332,327979dd. This indicates that this is a Projected Coordinate System.

    decimal degrees extent
    Notice the Extent has small numbers -26,333041?? starting with to decimals. This indicates that they are Decimal Degree measurement which is a Geographic Coordinate System
  3. Define the coordinate of your data by using the Define Projection tool (This tool is for datasets that have an unknown or undefined coordinate system defined)define projection
  4. After defining the coordinate system of the data, check against a Basemap if it is located at the correct place.add basemap
  5. Project the data using the Projection Tool (This tool is to change the dataset from one coordinate system to another)project tool

 

Georeferencing and Spatial Adjustment

 

Georeferencing

 

Provides a correct, real-world spatial reference to Raster or CAD datasets; which is either missing a real-world spatial reference or has an unknown spatial reference.

Georeferencing is the process of aligning geographic data to a reference dataset in a known coordinate system. This method helps to associate a physical map, raster or CAD document with a spatial location. When you Georeferencing a dataset, you define where the data is located using map coordinates. Georeferencing uses Control Points, that associates the data with a specific location on earth; which allow the georeferenced dataset to be viewed, queried and analysed with other geographic data.

During Georeferencing it is important to use correct Reference Datasets; raster or vector feature classes can be used as reference data only if the data has the correct spatial reference. Identify distinctive locations that are visible in both datasets, these will be used as Control Points. The control points link the original dataset that is being georeferenced to the reference data –  the first control point is plotted on the original dataset (data that needs to be aligned with the reference data) the second control point is then plotted on the corresponding location on the reference data. Corresponding Links are established from the control points, which will be used to align the original dataset with the reference data.

Spatial Adjustment

Like Georeferencing; Spatial Adjustment aligns the original dataset to a reference data, based on links between corresponding control points. The major difference between the two methods is the original datasets and the usage of the method; Georeferencing is used to re-create a missing or unknown spatial reference for Raster or CAD data while Spatial Adjustment is used to correct the alignment of editable vector data.

Data in GIS usually comes from different sources, which means the user is required to perform additional work to integrate and use the data together. Spatial adjustment is used to correct; inconsistencies between data sources, correct geometric distortions and align features together. There are a variety of adjustment methods that can be used to adjust all editable data sources. Another interesting task in spatial adjustment is the ability to transfer attributes from one feature to another.

There are three methods for performing spatial adjustment: transformation, edgematching and rubber sheeting.  The edgematching method is typically used for connecting the end points of features with each other, rubber sheeting is best used for aligning minor geometric adjustments; this method stretches, shrinks and reorients features to match the reference data and the transformation method is like the transformation method used in georeferencing; it will shift, scale, rotate and skew the data if necessary.

 

The table below shows the major differences between the two methods above.

Georeferencing Spatial Adjustment
The process of aligning data with missing or unknown spatial reference to reference data in a known coordinate system Editing functionality for aligning data with a spatially accurate reference dataset
Transformation Method Transformation Method

Edgematching Method

Rubber Sheeting Method

 

Works Out of the Edit session Works in the Edit Session
CAD, Raster Imagery, Aerial Imagery Feature Class or Shapefile (editable vector data)

Common Errors Due to Inconsistency in Data

georef_cad
Error showing an un-georeferenced CAD Layer
inconsitency
Errors showing Features Classes (vector data) that do not align to the Reference Data

 

Quick Easy Steps for Correctly Aligning CAD/DWG Data

  1. Assign GCS (Geographic Coordinate System) to the CAD/DWG file (WGS_1984) in ArcCatalog, if it has no spatial coordinate system / unknown coordinate system.unknown coordinates
  2. Load a Basemap for reference purposes, it is advisable to choose the South Africa Cadastre Basemap available on ArcGIS Online Basemap especially if you are using CAD/DWG Files.basemap
  3. Georeference the CAD/DWG file, using the reference data (data in the correct geographic location that has the correct Spatial Reference i.e. farm portions).georef
  4. When Georeferencing; it is vital to have two distinctive locations in both the CAD/DWG File and the Reference Data, these two distinctive locations will be used as Control Points.georef_control_points
  5. Export the georeferenced CAD Feature to a Feature Class place it in a file geodatabase once georeferenced, first create a new file geodatabase if necessary. Working with Feature Classes is recommended especially if you must spatially adjust the data after Georeferencing.
  6. Adjust the feature class by using Spatial Adjustment (use the Affine method)spatialadjustment
  7. Use the Define Projection tool to define a coordinate for the feature class that perfectly aligns with the Reference data.
  8. Project, it accordingly and assess the resultsresults

Limitations of Georeferencing CAD datasets

Georeferencing a CAD dataset is limited to one- and two-point transformations using the similarity transformation method:

  • one-point transformation comprises one link and moves the dataset
  • two-point transformation comprises two links and moves, rotates, and scales the dataset uniformly

Both methods preserve the shape and angles of the CAD dataset, however, the aspect ratio (the ratio of the width to the height of an image or screen) of the CAD drawing is distorted

Spatial Adjustment of CAD datasets

The spatial adjustment method maintains the aspect ratio of the CAD drawing and prevents skewing to the x- and y- axes. However, it should be noted there will be an inherent deformation of the aspect ratio, from the georeferencing step.

 

 

 

 

Contributor: Busisiwe Ngobe

 

Understanding Survey Diagrams

Surveying is all about measuring distances, angles and positions on or near the surface of the earth. Surveyors use mathematical techniques to analyse field data. Survey measurement relies on understanding two basic scientific, accuracy and reliability.

Types

  • Plane surveying: Earth surface is considered a 2D plane with x-y dimensions.
  • Geodetic surveying: Earth surface is considered spherical (ellipsoid) 3 dimensional

Classes

  1. Preliminary survey (data gathering): is the gathering of data (distances, position and angles) to locate physical features (rivers, roads and other structures) so that data can be plotted to scale on a map or plan, also include the difference in elevation so that contour could be plotted.
  2. Layout survey: Marking on the ground (using sticks, iron bar or concrete monuments) the features shown on a design plan features: – Property lines (subdivision survey). – Engineering work (construction survey). – Z-dimensions are given for x-y directions.
  3. Control survey: used to reference preliminary and layout surveys.
  • Horizontal control: arbitrary line tied to the property line or HWY centre or coordinated control stations.
  • Vertical control: Benchmarks: points whose elevation above sea level is defined accurately.

Different methods of surveying

  1. Topographic survey: preliminary surveys used to tie earth surface features.
  2. Hydrographic survey: preliminary surveys tie underwater feature to surface control line
  3. Route surveys: preliminary, layout and control surveys that range over a narrow but long strip of land (highways, railroads, electricity transmission lines and channels).
  4. Aerial survey: preliminary and final surveys to convert an aerial photograph into scale map using photogrammetric techniques.
  5. Construction survey: layout of engineering work.
  6. Built survey: preliminary surveys tie in features that just have been constructed
  7. Property surveys: preliminary, layout and control surveys determine boundary locations.

Unit of measurement

There are two main measuring systems:

English system and Metric system (SI units).

  • Angles are measured by: Degrees, minutes and seconds.
  • 1 revolution = 360 degrees, 1 degree = 60 minutes and 1 minutes = 60 seconds

http://faculty.kfupm.edu.sa/CE/hawahab/WEBPAGE/CE260/NOTES/1CE260%20CH%20%201.pdf

Types of survey diagram

  • Servitude diagrams (powerlines, pipelines or municipal services) for registering servitudes over an existing property.
  • Lease diagrams for registering long leases over portions of properties.
  • Consolidation diagrams when it is required to consolidate several individual properties into one, taking out certificates of consolidated title.
  • Mineral diagrams to register mineral rights separately from the land rights.
  • Mining title diagrams for registering the right to extract minerals from the land.

http://csg.dla.gov.za/diagram.htm

Coordinate systems

SA_Coordinate

Angles of direction

Directions are measured clockwise which is the opposite for GIS data (counter clockwise).

Azimuths

  • Azimuths are horizontal angles measured clockwise from any reference meridian.
  • In a plane surveying, azimuths are generally measured from north/south starting at 0⁰.
  • Azimuths are used advantageously in the boundary, topographic, control and other kinds of survey, as well as in computations.

 

In the south azimuth system, the angles are measured clockwise from south 0⁰.

south azimuth system

 

ArcGIS by default, accept angular measurements of the polar direction measuring system

Polar angles are measured counter-clockwise from the positive x-axis, east 0⁰.

c_clockwise

Bearing

  • Assumes that total station is set up at points A, B, C, D, E, F and G; bearing read on lines AB, BC, CD, DE, EF and FG.
  • AB, BC, CD, DE, EF and FG are forward bearings and the inverse will give backwards bearings
  • Both the forward and backwards bearing should have the same numerical values.

One can change the direction measuring system and angular units the editing tools use on the Units tab of the Editing Options dialog box.

http://moodle.najah.edu/pluginfile.php/47169/mod_resource/content/0/Angles_Azimuths_Bearings.pdf

http://desktop.arcgis.com/en/arcmap/10.3/manage-data/editing-fundamentals/about-direction-measuring-systems-and-units.htm

 

 

 

 

Contributor: Lutho Mbeki