How To: Calculate the reference scale for import CAD annotation
Instructions provided describe how to calculate the reference scale for import CAD annotation. CAD text is defined in map units. ArcGIS annotation is defined in points, which are defined as a viewing size of 1/72 of an inch. An ArcGIS reference scale is required to define a correlation between the text sizes from CAD to display points in ArcMap.
The Import CAD Annotation tool uses the reference scale to determine the size of the annotation in ArcMap. When a map is printed or viewed at the reference scale, the text appears at the target size in points.
The following is the procedure to calculate the proper reference scale. This algorithm creates a ratio between the initial text size in map units and the target size in points relative to the reference scale. A sample application is available, by way of the Related Information section below, that performs this calculation.
The following is a description of the steps needed to calculate the reference scale manually.
- Determine the target size of the resultant ArcGIS annotation in points [Anno_Points] for a given text size in map units [TextMapUnits].
- Convert the [TextMapUnits] to inches [TextMapUnits_Inches].
The method to convert the text size in map units to inches varies based on the coordinates of the source data: geographic, meters, feet, and so forth.
- Once the text height in map units is converted to inches, calculate the reference scale using the following equation:
ReferenceScale = (TextMapUnits_Inches * 72) / Anno_Points