By Dennis Collin
I recently received a question on getting annotation and plot scales to display as expected when the drawing units have been set to metres. AutoCAD users in most of the world tend to use millimetres as their drawing units, particularly when producing drawings of mechanical parts, components and building layouts. However, when working on larger features like roads, bridges and site plans, working in millimetres is not practical as it results in rather long and easy to misread numbers.
Surveyors, civil engineers and GIS users tend to work and think in terms of metres, this means when setting up templates, sheets and annotation scales should be set as the default drawing units.
Once set, annotation scales need to be defined to also think in those terms. The default ratio on the metric template is working upon the assumption that millimetres are the drawing unit and as a result to get items like linetypes, text styles and the correct plot scales users modified accordingly.
Firstly, within the UNITS command, set the Insertion Units to be metres, a typical precision is 3 decimal places (i.e. a millimetre). To get AutoCAD to update all the annotations correctly, users can add or edit the drawing scale list to include typical scales appropriate for site plans, survey drawings and mapping.
A title sheet though, typically in Paper Space, is often defined in millimetres. If using a title sheet as a block remember to draw it in millimetres and have the block units set to the same type. Remember elements placed in paper space are not affected by annotation scale.
Typical scales are 1:500, 1:1250 etc, but when setting the paper units to drawing units ratio remember that metres are being used to millimetre paper space units. So, the ratios in this case would be, 1-to-1 for 1:1000 and 1-to-2.5 for 1:2500 and 1-to-0.5 for 1:500 i.e. move the decimal place by 3 digits. By doing this it shouldn’t be necessary to manually scale drawings by bespoke scales to correct for the different units used in drawing.
By setting up a drawing this way, system variables like DIMSCALE and LTSCALE can be left at the default value of 1. Also, the incumbent linetype definitions should work as expected with the larger scales scaling the line patterns to be plottable on the sheet. It is also possible to link view titles to the viewport scale with a field.
Users should remember to show the value 1:500 to ensure the field format is set to display ‘Use Scale name’.
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