Model Generation and Data Processing

Importing of data from various sources into a comprehensive model

Noise modeling, at least the city wide variety, has become an exercise of taking available data from multiple sources and melding them into a single model. Elevations often are supplied by the surveying administration as a spot elevation file either describing the ground or the surface as seen from an aircraft. Both sets of data have their place, the elevations describing the ground are used as the base model where other objects are placed on, the raw version if imported for the buildings will deliver the heights of the buildings. Often the road administrations have very good data of the alignment of the roads, however it does not hurt to check with companies dealing with road data for navigation systems. These files often lack the third dimension or have questionable elevation information. Therefore SoundPLAN is set up to import the “raw” elevations restricted to the road surface, triangulate the data unfiltered and then set the road coordinates on top of this triangulated mesh. This has proven to yield the most accurate results. Buildings are most often available from the city planning authorities and can be imported from a DXF file or in recent time may be available from a GIS system in the format of Shape Files. All data can be imported only if they are set within the same coordinate system. SoundPLAN allows coordinate transformations at import time or any time later on to make sure data are using the same coordinate system.

Build the basis, the elevation model

Elevation data from aerial surveying often come with a resolution of an equivalent of 1 coordinate for each square kilometer. For a small noise study this may be feasible, for a noise study of a mega city or an entire province  a million coordinates per square kilometer will overwhelm the program and will lead to very long calculation times. As with everything in live compromises between speed and accuracy are needed, here the solution is the tolerance. When importing the data we can tell the program how accurate the elevation information needs to be if we can allow a tolerance of +/- 0.2 meters, the program will filter out coordinates it can spare and still at any given point in the model have less or equal deviations than 0.2 meters. SoundPLAN does this by repeatedly triangulating the data and checking what data can be taken out of the model without violating the set accuracy.  As this import and filtering may be time consuming, especially for province or country wide models, SoundPLAN offers the possibility to copy all unfiltered elevation files into a separate folder and execute the triangulation/filtering as a batch process off line.

Add objects to the basis, import from various sources

In SoundPLAN all models are created in the GeoDatabase. The data themselves are organized in the form of data objects of various types, all (except some very basic elements like spot elevations) have the capabilities to be made up of coordinates and attributes. All these data objects are saved to Geo-Files. SoundPLAN has no restrictions of how many objects of what type are gathered in these Geo-Files. Along with background bitmaps and the triangulated elevation data, they form a Situation, a scenario that describes a region or a planning stage. An unlimited number of these Situations can be created within a project.

When spot elevations are imported, they are imported as spot elevations until they are converted into the triangulation that will form the basis of the import and also the calculation. The triangulation file is not completely static, some changes and amendments can be made later on. When the basic filtering and import of the data deliver a triangulation that covering the entire model, the roads are not explicitly part of it. In subsequent steps we can refine the model by eliminating the data points on top of the road, importing unfiltered data for generating a local triangulation of the spot elevations on the road itself with coordinates on the master alignment and also on the edges of the road. These alignment and road edge data now are so accurate that it would be a shame not to include them into our basic triangulation. Similarly we can improve other objects such as railway lines and buildings and include the information in the triangulated mesh file.

Import traffic data to an existing system of roads

Traffic information usually is provided by a different planning authority than where we got the exact road alignments from, therefore we have included provisions to import traffic data to already existing objects. For the data to find the correct object and location we need an attribute that can be found in both sets of data. We find it in the form of the “road Section”, which can be seen as “road xyz from x-point to y-point” but it could also be more formal in the form of road x between node A and node B. During the import it is paramount that we synchronize and after import it is highly recommended to use the SoundPLAN Attribute Explorer to make sure that every road section has been dealt with. The Attribute Explorer allows the user to sort the objects in accordance to one of the attributes, so we easily find the road sections that have 0 vehicles, which most likely is a mistake in the data. Finding and marking roads with extremely low volume (less than 100 per day) and then eliminating these roads is also quickly done.

Auto-detection of bridges

When importing data automatically, it is of great help if the model has an auto detect function for bridges. SoundPLAN is able to follow the road alignment and scan the terrain next to the road and find where there are bridges in the model. Bridges are marked in the data as they permit noise to travel underneath and also over the bridge. If we do not mark a bridge as a bridge, the bridge will be viewed as a solid wall with the road on top.

Checking and verifying the model

None of the models can be simple expected to be simply imported and then run, verification of the model and checking it for errors is always a necessary step on the way. SoundPLAN has several tools to your disposal for this task. A formal check is the pre-flight that checks if the model geometry makes sense. It will find errors and write them into a log file where you can browse the warning and error messages and directly jump to the object in question. One of the errors the program is very sensitive about is little jumps in the elevation from coordinates that are close to each other. These errors cannot be detected by visual inspection in the 3D graphics or the 2D projection, the changes are too small. The effects however may be visible in the noise map if for example 2 coordinates are 0.1 meter apart with an elevation change of 0.3 meters. The program automatically calculates the incline of the road surface and inserts an “incline addition” to the basic emission level. Unchecked these errors are visible later on in the noise map.

The easiest check is to view a frontal projection of the entire morel. If coordinates are set to the elevation 0.0 they will be very visible as they stretch the elevation projection. Other checks involve creating buffer zones around the master alignment of the roads and checking where other objects (in general buildings) are colliding with this buffer. This half-visual check can be undertaken quickly for a large area. Another set of checks are involving the Attribute Explorer and scanning for buildings that are less than 2 meters tall or for roads with a width of 0.0 meters. Many items can be searched for quickly by selecting a single attribute, sorting all objects in accordance to this attribute and inspecting the extreme values.

Structured data storage (Situations and GeoFiles)

SoundPLAN data as mentioned before are saved to GeoFiles with the Situations as the label for a scenario. SoundPLAN can handle as many GeoFiles and as many Situations as your project requires. The same GeoFile can be included in a multitude of Situations, likewise you can have all situations refer to the same triangulated mesh file. GeoFiles and also Situations can be copied with Drag and Drop, if you modify them, you can save them under a new name, this make creating variants a snap. Keep the basic model the same and only make a copy of the file that contains the roads to change the traffic volume for a future planning stage. By only copying and modifying what is needed, you can avoid creating redundant files or projects that are all very similar but will create a  headache if error corrections must be made later on in redundant sets of data. The Situation Manager of the GeoDatabase keeps track of your files and facilitates copying, moving, renaming of the files. You do not have to rely on the operating system to find your data.

Support for big projects

Big noise modeling project have their challenges. If a project is small, you can visually check the project area and have an understanding of the geography, with a province wide noise map it is impossible to “know” the entire area. Sandwiching the SoundPLAN model data with a bitmap from Google Earth helps understand the situation. In the 32 bit version of SoundPLAN there is an interface directly to Google earth (when Google Earth is available as a 64 bit application it will also be available in the 64 bit version). For the interface to work, the coordinate systems must coordinate between the SoundPLAN project and Google Earth. SoundPLAN has a library of coordinate systems used worldwide, the UTM coordinate system that Google uses is part of it.

Tiling

When a project is getting bigger than a couple square kilometers, it is helpful to subdivide the project into smaller units. We call this process Tiling. Tile sizes are user selectable, it is even possible to have multiple tile definition within a project. A road network may be managed with tiles of 10x10 kilometer while buildings can be best edited with a tile size of 1x1 or 1x2 kilometers. In the Situation Manager of the GeoDatabase simply convert the “normal” project into a “tiled” project by requesting the new structure and supplying a bitmap that allows you to recognize the section of the project you want to work on. The GeoDatabase will load the areas tile by tile with the possibility to edit the data within one or multiple tiles. Inside the data editor you can move the mask and some data are sent to the disk and others are re-loaded.

The tiles also make it easier for the calculations and the post processing in the Graphics. For the calculation it can be assumed that a tile size of 2x2 km is optimal. For most of the calculations it is sufficient to have the tile that you are currently simulating loaded plus a secondary ring of 8 tiles around the tile you are currently calculating. The calculations have automated the loading/calculation/saving the results and the tile manager will show the status of the tiles (which one is edited, calculation, has some problems…)

Off Line import of data from external files

The host town for the SoundPLAN development team only has only 35 000 inhabitants but the amount of data for such a medium sized project can be a little bit intimidating. We were given the elevation model as a set of 385 file amounting to 2.66 gigabytes of data. The biggest project we have dealt with is the END train noise map for the entire country of Germany. Defining the import parameters, filtering the elevations etc. is no longer sensible on line with a project like this, therefore the Calculation Core with its possibility of Batch Processing has been harnessed into providing the muscle here.

Work with an Oracle Database

For a relatively big project in the greater Frankfurt (Germany) area it was determined that the project would benefit from having mode geographical selection tools that the GeoDatabase can supply. The project involves over 2 million buildings and 36 GB of terrain data. An Oracle Database was selected as the tool of choice, the extra capabilities to this form of a data storage came in the form of the SQL server. The initial step of setting up the Oracle database involved setting up a correspondence table between what SoundPLAN needs and whet the GIS could supply.

Full integration of indoor and outdoor modeling

SoundPLAN is unique in its modeling capabilities for industry noise. Indoor and outdoor modeling are completely integrated. You can model the noise inside the factors and then define the transmissions through the outer walls to get a comprehensive noise model for the environmental noise. The industrial building is an addition to the customary point, line and area sources.

Full integration of aircraft noise

SoundPLAN is unique in its modeling capabilities as it is capable to model aircraft noise in accordance to the internationally recognized standard ECAD Doc 29, third edition. In addition to modeling the aircraft noise SoundPLAN can model the IPUs, air conditioning for the airport, transportation noise, engine run-up-pens and all other frequency dependent noise sources that normally cannot be handled in traditional aircraft noise models.

In this picture it is clearly visible that distributed spot elevations produce a superior 3D image than the triangulation of very many points on an elevation lines. The top of the mount is not defined by the elevation lines.
The picture shows the raw data from one of the tiles that were imported from an elevation file. The first picture in this series shows the unfiltered infomation of the valley.
The picture above shows the data that are actually left after the filter has eliminated over 90% of the data.
A 3 D picture of the triangulated surfaces shows a good representation of the terrain.
The differences between the original and the filtered data show that the data points are all within the tolerance with many of them having much smaller deviations than originally allowed.
The result of an automatic bridge detection run as an insert on an aerial photography