TAP Coverage Study Performance
Q: How can I improve the speed of coverage studies run with TAP?
A: The Terrain Analysis Package (TAP)™ software provides great flexibility to enable you to control all the parameters of coverage studies. You can set these parameters to provide the best combination of speed and detail for your studies.
TAP provides several types of coverage study options you can use. The choice between Tile and Radial studies will affect the time it takes for the study as well as the final presentation of the study.
For example, a Radial study using 360 radials out 50 miles, with calculations every tenth of a mile will compute 180,000 field strength values, but only has to read the topographic elevation data for the 360 paths. Each field strength calculation on a radial uses the topographic data for that radial out to the distance needed. On the other hand, a Tile study out 50-miles from the base station, every quarter of a mile computes 160,000 field strength values, but requires the topographic elevation data for 160,000 paths.
You should select the type of study which is best suited to your need. For example, suppose you have five potential repeater sites you want to evaluate to determine the best location. One suggestion would be to use a radial study from each site for the initial evaluation to get an idea of which site will provide the coverage you are looking for. Then you may want to use a more detailed Tile study for the final presentation of the site you select.
The Area Coverage Performance article contains some examples and benchmarks for different types of studies.
How big is the area you want to study? When you set the range of the radials or the tile area, you want to be sure to include all the areas of interest. In some cases, for large areas, there may be significant portions that are included where coverage is unimportant. For example, if you have a repeater site located on a mountain to provide coverage to three near-by communities, you could do a single study to include the whole area. But if much of the uninhabited regions between the towns is irrelevant to your coverage (especially where there are no major roads or highways), it might be better to set up three smaller studies, one enclosing the area for each town. HDCoverage functions make this easy to set up and run. Then you can combine the individual studies on a single plot, using the HDMapper function.
How much detail do you need for your study? A study that is a hundred miles square, with field points computed every hundredth of a mile results in a hundred-million field calculations. That may be more detail than you really need over the entire area. As suggested above, using smaller study areas for that level of detail may give you a more usable result. If you want to see the coverage over a 100 x 100 mile area, with extra detail in areas of interest, such as towns or highways, you can run a single large study, with less detail (maybe computing the field strength every half mile, for 40,000 tile points), then a separate smaller study with more detail for each of the towns.
If you only need the field strength at numerous discrete locations (such as a SCADA system, telemetry points, pipeline valve stations, etc.) you can use the HDCoverage Target Study function. This will compute the field at the specific desired points without spending the time to compute an entire Tile or Radial study.
What field strength levels do you want to show from the coverage study? It is important to understand that once you have run the coverage study you can plot different field strength levels without the need to run the same study again. When you run the study, the computed results are saved in a database. You can plot the same study showing the locations for different field strength levels using that database. The article on Required Field Levels discusses the importance of selecting the appropriate field strength levels for the hardware and environment that are most suited to your communications system. Often you will want to show various levels of signal for different mobile hardware units, different loss values, “best-case” and “worst-case” comparisons, etc. As long as the system parameters stay the same (fixed and mobile antenna heights, frequency, power, etc.) you can show the coverage areas for various signal levels representing different conditions by plotting the same study (in HDMapper) without the need to run a new study for those conditions.
What changes do you want to make to run a new study? If certain parameters are changed, you can still use the results from a study as a starting point, rather than running a completely new study. For example, suppose you ran a large study with an Effective Radiated Power (ERP) of 100 Watts, using a particular directional antenna with the major lobe oriented at an azimuth of 45 degrees. If you want to run a new study from the same site, with the same antenna height and operating frequency, you can use the Field Recalculation function. The program enables you to open the old study and specify the new ERP, antenna pattern, and orientation. The program then reads the results of the original study and adjusts the field strength results based on the differences between the power and gain values in the original and the new study. As long as the geometric factors of the path (base and mobile antenna heights, and the frequency used for Fresnel clearance calculations) don’t change, you can use the Field Recalculation function to try numerous “What if?” scenarios with different power levels and antenna configurations.
What kind of topographic elevation data do you have for the area? The topo data step value you select determines how much detail the program will have from the topographic elevation data. The detail is important to be sure the program considers hills or ridges that could obstruct the path and affect the computed signal strength. Setting large step values can result in significant topographic features being missed.
But setting the topographic step value too small can slow down the study unnecessarily. Remember the discussion about the path elevation information for Tile studies. Topographic elevation retrieval becomes a dominant part of the time used for the study, so choosing an appropriate value is important. The resolution of the topographic data you are using is an important consideration
For example, suppose you have 3-second elevation data for the area under study. The spacing between elevation points in the topographic data files is 3-arcseconds, or about 250 feet (depending on where you are in Latitude). Setting the topo data step to a value in the range of 0.1 or 0.05 miles will get just about all the detail available in the file. Trying to get more topographic detail by setting the value to, say, 0.01 miles will cause the program to spend a lot more time reading the data files, but not provide any more significant detail for the study.
What surface feature information do you want to include in the study? TAP Surface Feature files enable you to include information such as buildings, vegetation, or other types of “clutter” on the surface, effectively increasing the elevation above the topographic values. This is another example where you can use general information for preliminary studies (as in the repeater site selection example above), and use more detailed information as you refine the study.
TAP uses the Surface Feature files you create to include the effects of ground clutter in the field strength calculations. Including detailed information about the potential obstructions will enable TAP to consider those features. Since each obstacle is considered for each topographic elevation data point on each path, including the Surface Feature files can have a significant effect on a study.
One important consideration is to divide the Surface Features into geographically-organized files. Having all the features in one large file will slow down a study you are doing in the Dallas area if the file includes obstacles in Denver. Since you can include as many Surface Feature files as needed for any study, it makes more sense to create several smaller files that can be included as applicable for studies in different areas.
The number of records in each file is also a factor. You may want to create very detailed files with records for individual building or vegetation in parks, etc., to use in your coverage studies. But if you are running numerous preliminary or “What if?” studies, you might also want to create a separate file containing a few representative obstacles. One TAP user imported thousands of records from a city planning database, which provided incredible detail in the studies. You can also create generalized obstacles in a separate file showing one large obstacle that could represent numerous buildings of similar height in certain sections of the city. Once again, using the more generalized information for preliminary planning studies and the more detailed data for the “fine-tuning” of the design is a good balance to get the best performance from the software.
Field strength studies involve many inter-related parameters and settings. Usually the best way for SoftWright Support to offer more specific suggestions for improving performance in your coverage study is for you to email the Task files used for the study. This will provide more detail and allow your study to be setup and run on one of our test machines to see if there are any other suggestions that might improve the performance.
The TaskZIP function is a convenient way to collect the files and send them to SoftWright Support.
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