ArborShadow Accuracy
Sun Position Calculation
One of the most important functions necessary for accurate shadow plotting is calculation of the correct position of the sun for a given earth position, date and time.
The suns height in the sky (its altitude) and its lateral position (azimuth) are the necessary calculations required and both of these require an accurate declination value. So to ensure the ArborShadow method is working to a reasonable tolerance I check a few random results against three other calculation tools which are available free to use on the internet.
The results of the tests are displayed on the following links:
Sun Declination
Sun Azimuth
Sun Altitude
Shadow Plotting
The ArborShadow shadow plotting calculation method works to an accuracy tolerance of +/- 250mm. This tolerance is subsequently transferred into the shadow area calculation and also into reference-area area calculation and area of overlap calculation. However, how the tolerance applies itself to a polygon is difficult to predict due to the variable size, area and orientation of the shadow (the tolerance only limits the east-west dimension).
I carried out a series of simple tests to determine how the tolerance actually affects the area calculation. To do this I employed the use of AutoCAD to calculate the area of an exported shadow, reference object and overlap area.
This value was then compared to the value produced by ArborShadow and the data processed by MS Excel spreadsheet.
To use AutoCAD for this purpose the exported script data (to produce a polygon) was converted into a Region Object which could then have its area determined.
The results of the tests are displayed on the following links:
Single Tree Shadow Area
Reference Area
Overlap Area (single tree)
Overlap Area (two trees)
Overlap Area (Multiple tree)
One of the most important functions necessary for accurate shadow plotting is calculation of the correct position of the sun for a given earth position, date and time.
The suns height in the sky (its altitude) and its lateral position (azimuth) are the necessary calculations required and both of these require an accurate declination value. So to ensure the ArborShadow method is working to a reasonable tolerance I check a few random results against three other calculation tools which are available free to use on the internet.
The results of the tests are displayed on the following links:
Sun Declination
Sun Azimuth
Sun Altitude
Shadow Plotting
The ArborShadow shadow plotting calculation method works to an accuracy tolerance of +/- 250mm. This tolerance is subsequently transferred into the shadow area calculation and also into reference-area area calculation and area of overlap calculation. However, how the tolerance applies itself to a polygon is difficult to predict due to the variable size, area and orientation of the shadow (the tolerance only limits the east-west dimension).
I carried out a series of simple tests to determine how the tolerance actually affects the area calculation. To do this I employed the use of AutoCAD to calculate the area of an exported shadow, reference object and overlap area.
This value was then compared to the value produced by ArborShadow and the data processed by MS Excel spreadsheet.
To use AutoCAD for this purpose the exported script data (to produce a polygon) was converted into a Region Object which could then have its area determined.
The results of the tests are displayed on the following links:
Single Tree Shadow Area
Reference Area
Overlap Area (single tree)
Overlap Area (two trees)
Overlap Area (Multiple tree)
