Capricorn: Dec.22-Jan.29 The Sundial Primer
created by Carl Sabanski
Capricorn: Dec.22-Jan.29

The Sundial Primer Index

Dialling with QBASIC - Mac Oglesby - Vertical Declining Monofilar Standard Time Sundial

"Following my investigation of horizontal civil time dials, I decided to try to design and build a large vertical civil time decliner. But first I made a small paper and plastic model, which was on the cover of Compendium 9-1 March 2002. See attached file VertDecliner6x10.jpg (Figure 1). My memory isn't clear exactly how I did that dial face, but probably, after determining the equivalent horizontal plane for the declining wall of our house, I used one of my QB programs for horizontal civil time dials having unfolded analemmas.

The large vinyl "rainbow" dial face was drawn using the QB program VDSTP11x.BAS. The DeltaCad file VDSTP11x-2.dc shows the output after running the txt file through CNVXXXX.EXE, opening the resultant dxf file in DeltaCad, and changing the line weight of the whole-hour lines. File VST0204E.dc shows the almost finished dial face. Wanting to use color bands for easier date reading but not being clever enough to do those color bands on my computer, I enlisted the help of daughter Alice. She created the file VST0204E.pdf, as well as the Illustrator file which went to the FastSigns shop for printing on vinyl.

The attached zip file (Rainbow1.zip) includes the QB program and two .dc files.

Compendium 10-3 September 2003 has my article "A Vinyl Sundial Face" with some remarks about this dial."

Figure 1 shows an example of a sundial that can be made. This is a model made to test the design before the final sundial was constructed. Making a model of any sundial is a good idea as it is inexpensive and will help to find errors in the design before a lot of time and money is spent on the construction of the final sundial.

Figure 1: Vertical Declining Monofilar Standard Time Sundial Model

Figure 1: Vertical Declining Monofilar Standard Time Sundial Model

Vertical Declining Monofilar Standard Time Sundial - VDSTP11x.bas

This program is called a "Horizontal Monofilar Sundial". Monofilar refers to the fact that a single piece of string is used for the shadow casing edge or style. The curved lines are the "unfolded" analemma and allow for the correction of the Equation of Time. The circular "date arcs" indicate where to read the shadow to get the correct EoT correction. The hour lines can also be corrected for longitude.

You can get the QBASIC program as well as two DeltaCad files here.

Figure 2 shows the program when it is opened in QBASIC. Take the time to read through the comments. There are a few parameters you need to modify to have it design a sundial for a particular location. These are highlighted by the red rectangle and start on line 12 and continue for a total of 9 lines.

The first line defines the name of the text file and gives the location where it will be written.

filename$ = "c:\VDSTP11x. txt"

"c:\VDSTP11x.txt" can be changed to place the file in any directory and give it any name. "c:" defines the disk and is likely not going to change. The path is set to the root but should be changed to a more appropriate directory. Remember to use the backslash "\". The file name "VDSTP11x" is appropriate unless you would like to give it another name.

The following lines, 13 to 20, need to be modified to define the sundial parameters as follows:

PHI = 42.85 - 'latitude of the dial in decimal deg. (0 < latitude < 66.5)
LocLong = 72.55 - 'longitude of local meridian (decimal degrees, west +)
TZM = 75 - 'longitude of standard time zone meridian (decimal deg.)
DECDIAL = -46.56 - 'Declination of dial from south (west +)
EoTyesno = 1 - 'Want Eot correction? (1=yes, 0=no)
STRT = 1 - '1st of which month to start (Jan=1,Feb=2,...Dec=12)
Min = 375 - 'radius of inner arc (outermost arc radius = Min+366)
SPZ = .25 - 'step size for hour lines (.5 draws half-hour lines)

All the values in red can be changed if required to meet your specific design requirements. Note that repeating decimals for "SPZ" may produce poor results.

Figure 2: Vertical Declining Monofilar Standard Time Sundial QBASIC Program

Figure 2: Vertical Declining Monofilar Standard Time Sundial QBASIC Program

"For latitudes greater than 0 and less than 66.5, this program draws a vertical declining dial face which has date arcs and 'unfolded' analemmas. As a guideline, use this: -75 < declination < 75. Longitude and Equation of Time corrections may be included. To avoid any longitude correction, input same values for longitude and time zone. Input 0 for EoTyesno to turn off EoT correction. Lines are drawn for noon and for the sunstyle

Only some lines appear on the screen, but all data for dial lines are written to a .txt file. Fer de Vries' program CNVXXXX.EXE" may be used to create, from the .txt file, a .dxf file for use by a CAD program such as DeltaCad. Algorithms published by Fer de Vries are used to calculate EoT and solar declination."

When the program is run the second screen you will see is shown in Figure 3. The sundial configuration data is shown here and can be checked. If there is an error complete running the program and then start again to make any necessary changes. Also note this screen include additional information that should be recorded including:

Equivalent latitude
Hour angle of the substyle
Total longitude correction in minutes of time
y-axis to substyle angle

Figure 3: Vertical Declining Monofilar Standard Time Sundial Configuration Screen

Figure 3: Vertical Declining Monofilar Standard Time Sundial Configuration Screen

After the program run is complete the sundial is drawn on the screen although it will not be complete. This is shown in Figure 4 and the missing date arcs can be clearly not seen. The substyle can be seen in the figure. The notes at the top of the screen are not saved in the text file and should be read before exiting.

Figure 4: Vertical Declining Monofilar Standard Time Sundial - QBASIC Screen Output

Figure 4: Vertical Declining Monofilar Standard Time Sundial - QBASIC Screen Output

After the text file is created use the program CNVxxxx to convert it to a DXF file. Figure 5 shows the sundial when the drawing is opened in DeltaCad. The line weight of the whole hour lines has been increased. It may appear that portions of some lines are missing but they are not. They can be seen if you zoom into the drawing. The cross is the centre of the sundial and the point from which the monofilar gnomon will originate and follow the angle of the substyle.

Figure 5: Vertical Declining Monofilar Standard Time Sundial DXF File Opened in DeltaCad

Figure 5: Vertical Declining Monofilar Standard Time Sundial DXF File Opened in DeltaCad

The above figures show the sundial drawn using the default values in Figure 3. Figure 6 shows the completed drawing for the sundial shown in Figure 7. The hour numbers and text have been added and the boundaries for the dial plate have been defined. The comments regarding the missing lines given above apply here also.

Figure 6: Completed Drawing of the Vertical Declining Monofilar Standard Time Sundial

Figure 6: Completed Drawing of the Vertical Declining Monofilar Standard Time Sundial

Figure 7 shows the completed sundial in its intended location. A thin wire has been used for the gnomon. One end is attached to the dial plate and the other to the top of a post. The variety of colours used to fill in the spaces between the circular "date arcs" is what gives it the the name "rainbow" sundial.

Figure 7: Vertical Declining Monofilar Standard Time Sundial

Figure 7: Vertical Declining Monofilar Standard Time Sundial