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autodesk-forgeautodesk-viewer

Transform Edit2D Areas

I am using the Edit2D extension on an svf created from a 2D dwg file and have a question about transforms. The Autodesk.Edit2D.Polygon's that are created have a getArea() method which is great. However it's not in the correct unit scale. I tested one and something that should be roughly 230sf in size is coming back as about 2.8.

I notice that the method takes an argument of type Autodesk.Edit2D.MeasureTransform which I'm sure is what I need, however I don't know how to get that transform. I see that I can get viewer.model.getData().viewports[1].transform. However, that is just an array of 16 numbers and not a transform object so it creates an error when I try to pass it in.

I have not been able to find any documentation on this. Can someone tell me what units this is coming back in and/or how to convert to the same units as the underlying dwg file?

Related question, how do I tell what units the underlying DWG is in?

EDIT

To add to this, I tried to get all polylines in the drawing which have an area property. In this case I was able to figure out that the polyline in the underlying dwg was reporting its area in square inches (not sure if that's always the case). I generated Edit2D polygons based on the polylines so it basically just drew over them.

I then compared the area property from the polyline to the result of getArea() on the polygon to find the ratio. In this case it was always about 83 or 84 times smaller than the square foot value of the polyline it came from (there is some degree of error in my tracing system so I don't expect they would be exact at this point). However, that doesn't fit any unit value that I know of. So remaining questions:

  1. What unit is this?
  2. Is this consistent or do I need to look somewhere else for this scale?
Solution

  • Ok after a great deal of experimentation and frustration I think I have it working. I ended up looking direction into the js for the getArea() method in dev tools. Searching through the script, I found a class called DefaultMeasureTransform that inherits from MeasureTransform and takes a viewer argument. I was able to construct that and then pass it in as an argument to getArea():

    const transform = new Autodesk.Edit2D.DefaultMeasureTransform(viewer);
const area = polygon.getArea(transform);

    Now the area variable matches the units in the original cad file (within acceptable rounding error anyway, it's like .05 square inches off).

    Would be nice to have better documentation on the coordinate systems, am I missing it somewhere? Either way this is working so hopefully it helps someone else.