## 4 Methodology
### Calculate Satellite Positions  
It is essential for accurate satellite prediction surveys that the position of GNSS satellites in any constellation can be calculated at all times. The satellite ephemeris data (containing positional data, orbital information and satellite health) is broadcast in an almanac and this can be downloaded. Occasionally, there are adjustments to satellite orbits, so these almanacs must be kept updated. Importantly for the proposed methodology, software such as Trimble Planning also provides information on the azimuth and elevation to each satellite from a known observer point in the prediction results. Using this information to calculate pseudo satellite positions enabled us to avoid the need for a coordinate transformation from the earth-centred coordinate system of latitude and longitude to the projected coordinate system of the OSi digital mapping best suited for GNSS surveys [46], the Irish Transverse Mercator (ITM). To ensure the simulated satellites were not too close to the survey site (which would mean they would have an exaggerated field of view), they were simulated at a distance of 10 km from the campus. This simulated value was required in calculating the simulated coordinates. By developing a method that incorporates a pseudo distance that is shorter than the true distance, it allows us to avoid the viewshed restrictions identified by [33].  
For the initial tests, one day was chosen for the study and the time of the test was limited to between 10:00 and 17:00. A single point was selected in the centre of the campus and a table of all visible satellites and their elevations and azimuths at ten minute intervals from 10:00 to 17:00 was created (Figure 5a). In this image, the numbers in the table below each satellite ID refer to the elevation (always less than 90\({}^{\circ}\)) and the azimuth (between 0\({}^{\circ}\) and 360\({}^{\circ}\)). One issue with this process is that the Trimble Planning software only allows the latitude/longitude of the observer point to be specified in degrees and minutes, rather than degrees, minutes and seconds. This lowered the accuracy when specifying the position of the observer point, but planning of GNSS surveys does not require a high accuracy in positioning the singleobserver point and only influences the result when the point occurs close to the transition between two minutes (_i.e._, at 59 seconds.  
The data was exported into HTML format and then accessed and edited using an HTML editor. The geometric formulae for transforming coordinates X,Y and Z respectively to their pseudo positions X', Y' and Z' given the 10 km simulated range (\(s\)) and the measured azimuth (\(\theta\)) and elevation (\(\phi\)) calculated by Trimble Planning were  
\[X^{\prime} =s(\cos\phi\times\sin\theta) \tag{1}\] \[Y^{\prime} =s(\cos\phi\times\cos\theta) \tag{2}\]  
and  
\[Z^{\prime} =s(\sin\phi) \tag{3}\]  
This data was collated in a table and imported into ArcMap. An SQL query enabled the satellites present at any time of the day to be identified, isolated and visualised for analysis in the GIS. Figure 5b displays a 2D plot of all of the satellites from the GNSS constellations that were present over Maynooth University on Wednesday, 4 th May between 10:00 and 17:00 visualised in ArcMap.