Users may access the Workbook Settings dialog, shown in figure 11, from the Settings menu.
This dialog allows the user to set certain global variables such as the projection and air density lapse rates.
Openwind uses a meter grid and so can only support meter-based projections internally. When importing geographic data (i.e. with coordinates in degrees of latitude and longitude), these coordinates need to be converted to the current workbook projection. During conversion, the original geographic coordinates are replaced with the equivalent coordinates in the current workbook projection.
Openwind now has support for all meter-based projections including various state-planes, OSGB, Albers, Lambert and so on. Openwind will do datum transformations with varying results depending on the accuracy of the datum grids used.
When you first start a new workbook, the workbook projection is undefined. You can setup the projection and datum at this point in which case it is set for the workbook. In general, the workbook projection will be set when you load your first GIS layer. The logic for this is somewhat involved and so rather than explain it in words; we have provided the process flowchart in figure 13 below.
The flowchart ignores datum differences and datum transformations which are only partially supported at present. In general, it is assumed that all layers are using the same mapping datum unless it is specified in the projection information that comes with a file. In that case the user is offered the possibility of converting from the input datum to the workbook datum. However, this is a complex process and tends to rely on having access to grids of correction data. We have supplied the commonly available grids for North America (in the folder “DatumGrids” referred to in Preferences) but the user may need to source their own in order to carry out accurate datum transformations in other parts of the world. We consider support for datum transformations to be a work in progress so if you have feedback or helpful suggestions we would love to hear from you.
In the global values dialog, there is the ability to define a projection in terms of the parameters used. However, we expect users will prefer to load up a projection definition from a PRJ file that may have come with a different GIS layer but contains the information required to define the required projection.
The air temperature lapse rate is provided as an alternative to the air density lapse rate. The temperature lapse rate tends to be slightly more constant with increasing altitude and so is provided here for convenience.
The default turbulence intensity value is used to initialize the turbulence intensity for a Met Mast Layer. However, turbulence intensity (TI) data should be calculated and entered for every Met Mast Layer for every wind speed and direction. The easiest way to do this is to bring in time series met data in CSV format and get Openwind to process the time series into tables.
Detrend Turbulence Intensity For Use in Suitability and Loads - determines whether or not Openwind makes a detrended copy of the input turbulence intensity data in each met mast. Changing this value will trigger Openwind's detrending of all the time-series TI data in the workbook as well as replacing all the met mast tables.
The number of hours in a year is used to scale the energy capture to one year. Frequency table-based energy capture is probabilistic, and the total probability needs to be scaled to a number of hours.
The time-zone is used in calculating shadow flicker as well as scheduling turbines relative to sunset or sunrise. This needs to be set correctly in order for Openwind to know where the sun is at any time. It should be the base time-zone and not take account of daylight saving. This notes the time zone relative to GMT, e.g., New York would be -5 and Paris would be +1.
Openwind uses EPSG codes to define the internal workbook projection. Clicking on the EPSG box will invoke the EPSG selection dialog.
The save and load buttons allow the information in this dialog to be saved to or loaded from XML settings.
You can use the left text box search for EPSG codes by name or number or a mixture of both and candidates will show up in the list view below. If you are only interested in UTM zones then you can use the right-hand text box to search by zone number along with S for South (e.g. “22” is interpreted as 22 North whereas “22S” is interpreted as 22 South).
The workbook button will initialise this dialog with the current workbook projection.