How to link a double look up with a rectangle area

[Miralkong]

Hi guys. I want to achieve a visibility change effect with visibility and double look up. Detailed requirements are:

1. If the area of the rectangle is no less than 1.5 sm, then the solid hatch is visible

2. If the area of the rectangle is less than 1.5 sm, then the solid hatch is invisible.

as far as I know, I can link the length parameters and visibility parameters with double look up to achieve the effect that when the length is longer than a specific number or range, the visibility state can be changed. But how can I link the area of the rectangle with double look up? I tried to calculate the area with a length and a width constrain but failed to link the result with double look up.

So, is there anyone who knows how to achieve the goal? Thanks a lot.

[Libbya]

Have the linear parameters that stretch the length and width of the rectangle also scale a third linear parameter (I'd appropriately name it 'Area').  Make sure that the as-drawn length of the Area parameter matches the as-drawn area of the rectangle.  Use the Area parameter on one table with your area range values to switch the visibility state on the other table to turn on/off the hatch.  

If you need further assistance, post your block.

[Miralkong]

Tried like you said. But I did't understand the relationship among length, width and area linear parameters. I've uploaded the test block. Please help me figure it out. Thanks a lot.

[Libbya · Accepted solution]

As I said, the two length/width linear parameters should both scale the area parameter.  With both of them scaling the area parameter, provided it is initially drawn as a length that matches the area value of the rectangle, then as the width/length are adjusted, it will be scaled and its linear length will always match the area value.  You can then use that area parameter to control the visibility state.  See screencast:

[Miralkong]

Thanks a lot. I get the gist.