Create a wind or rose plot that crosses zero degrees in Grapher

Both wind diagrams and rose charts have bins that go from 0 to 360 by default. However, not all angle data is collected in this range.  For example, a data range of -180 to 180 could be used to represent a direction and deviation from 0. If you need to create a bin that crosses the 0 degree line, follow the instructions below.  

How to adjust angle data

  1. Click the File | Open command.
  2. Select the data file and click Open. The data will open in the Grapher worksheet.

originaldata.png
Original data displayed in worksheet.

  1. Highlight the Direction column.
  2. Click the Data | Data | Transform command.
  3. For the Transform equation, type C=IF(A>345,0,A). This assumes that the direction column is column A and the new blank column is column C. Replace the C and A with the appropriate columns for your data.

1sttransform.png
Enter the equation to transform all values greater than 345 to 0.

  1. Click OK. All values greater than 345 are replaced with 0.
  2. Click the Data | Data | Transform command.
  3. For the Transform equation, type C=IF(C<0,0,C). This assumes that column C is the new column from Step 5. Replace the C with the appropriate columns for your data

2ndtransform.png
Enter the equation to transform all values less than 0 to 0.

  1. Click OK. All values less than 0 are replaced with 0.

altereddata.png
Altered data displayed in the worksheet.

  1. Click the File | Save command to save the file.
  2. Click the File | Close command to close the file and return to the Grapher plot window.

Back in the Grapher plot window, create a new rose or wind plot.

  1. Click the Home | New Graph | Polar | Polar Rose Chart or Polar Wind Chart command.
  2. Select the data file edited above and click Open.
  3. Click on the plot in the Object Manager to select it.
  4. In the Property Manager, click on the Plot tab.
  5. Set the Direction column or Data variable column to the transformed column above, Column C.
  6. Set the Bar width bins type field to Custom bins.
  7. Click the Edit button next to Bins.
  8. Set the first bin to have a Minimum (>): value of -15.
  9. Adjust any other bin values and click OK.

The first bin will cross the zero line, displaying the desired data.

How to adjust the bin positions and width

Change the start angle (wind charts only)

Note: the steps below assume you want a bar width of 22.5 with the first bin centered on 0.

  1. In the Object Manager, select the wind chart.
  2. On the Plot tab in the Property Manager, set the Start angle to 348.75.
  3. Change the Bar width to 22.5.

wind_chart_custom_bins.png

Example Grapher wind chart with a bin crossing 0 degrees

 

Updated March 2024

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