Technical Tips

View Part 1

In the second issue of our series on 3D visualisation and GIS we are going to demonstrate some of the technical principles raised in first issue by way of an example using a project Spatial Vision is currently undertaking for Southern Rural Water (SRW).

This paper will build on these basic 3D principles as realised in ArcScene/3D Analyst and demonstrate how manipulation of the in-built properties of a 3D scene coupled with a little imagination can yield significant gains that assist internal understanding of corporate data and provide excellent visual tools for public interpretation.

Southern Rural Water administers groundwater diversions over a series of management zones across southern Victoria. Groundwater resources are tapped within these zones from a complex set of aquifers that are stratified vertically and are very often overlapping.

Managing these aquifers and specifically the diversions from them in the form of groundwater bores is one of SRW significant responsibilities. Clearly, in managing the current bore diversions, in assessing applications for new diversions and in providing information to the public SRW staff need significant understanding of the structure, configuration and spatial relationships of these, often, very complex aquifer systems.

In the past these complex systems have been mapped in 2D with mixed results in that the inherent 3D nature of these systems tends to make the standard planimetric map confusing, even to the acknowledged experts.

Glossary

Base Height – surface or value used to provide a vertical reference for a layer
Vertical Exaggeration - a multiplier that is used to increase the vertical component of a 3D scene.
Vertical Offset – a value used to float a layer above its base height reference.
Transparency – a percentage property that set the level of transparency of a layer enabling a see through effect.
Extrusion – a property set against polygon, line or point features that create a 3D object from the initial ‘foot print’

As part of SRW general information migration into an integrated GIS environment Spatial Vision was requested to conduct a small demonstration project across the Rosedale Groundwater Management Zone (situated in south-east Gippsland near Traralgon, Victoria) to demonstrate the potential for 3D interpretation and analysis and the possible integration of these capabilities into the corporate GIS that has been rolled out to SRW staff.

Figure 1: Rosedale Groundwater Management Zone  

SRW provided Spatial Vision with mean UPPER and LOWER depths of the deepest aquifer in the sub-zones of the Rosedale Groundwater Management Zone. This information was to be used to demonstrate the capability of the 3D software (3D Analyst/ArcScene) to assist in the visualisation of groundwater resources.

The first task in this project was to load each sub-zone polygon dataset into the ArcScene interface and set the 3D properties. Each of these sub-zones had been converted into a GRID or surface that where to provide base heights for 3D visualisation.

Figure 2: Rosedale Groundwater Management Zone  

The original polygonal sub-zones where then added and their base heights where set to the corresponding surface. A vertical exaggeration of X10 was applied (given the relative thickness of the aquifers compared to the extent of the sub-zones). Each sub-zone polygon was then extruded to a thickness equal to the aquifer thickness. Each of the sub-zones was symbolised with a different shade. This initial symbolisation and property setting created a 3D representation of the relative thickness and position of each sub-zone.

In order to provide a reference for the viewer several contextual layers where then added to the scene. These layers where: a digital terrain model, a road network, a hydrology network and major locality points.

The next visualisation issue to contend with was how to show the relationship between the groundwater aquifer zones and the surface features.

Figure 3 : Layer Properties - Base Heights  

Figure 4: Layer Properties - Extrusion  

In order to achieve a pleasing and meaningful result we added the terrain model first. This raster dataset was referenced to itself to create a representation of the surface terrain. A vertical exaggeration of X5 was used to emphasise the significant areas of terrain with the Rosedale GMZ. This 3D surface was then ‘floated’ above the groundwater sub-zones by applying a vertical offset of some 20km. Similar vertical exaggerations and offsets were applied to the road, hydrology and locality datasets.

Having done this we where then faced with the need to ‘connect’ the sub-zone surfaces to the floating surface terrain. To address this problem we extruded the points representing the major localities downwards through the groundwater sub-zone surface. This effect provided a connection between known points on the ground to corresponding locations on the sub-surface layers.

This simple example is an excellent illustration of the potential of a 3D environment to interact and visualise key corporate datasets. The next stage of this project will be to refine the techniques and procedures and then, if required, integrate this functionality into the SRW corporate GIS.

Figure 5: 3D surface over groundwater

Figure 6: Connecting the subzone through the groundwater subzone surface  

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Copyright © Spatial Vision, Monday, 16-December-2002