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Thread: Creating closed figures?

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    AUGI Addict sinc's Avatar
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    Question Creating closed figures?

    Is there a way to create a figure by entering courses from a legal description, then have AutoCAD adjust the courses so that they form a closed figure, but no single length, bearing, or angle is changed enough to affect the labelling of the resulting closed figure?

    For example, since land descriptions are generally given with distances specified to the nearest .01 feet and angles and bearings to the nearest second, this AutoCAD command would move lines and curves so that the figure closes, but all length adjustments are less than .005 feet, and all bearings and distances are changed by less than .5 seconds. Thus the resulting closed figure could be labelled using Land Desktop's labelling commands, and the resulting labels would be identical to those in the legal description.

    Assuming the legal description was correctly prepared, this should always be possible. A null solution would indicate an error in the legal description.

    BTW, I'm using Land Desktop 2004 with Civil Design and Survey modules. I'm thinking this task could be accomplished via a Lisp routine, but I'm hoping someone else has already gone to the brain-damage of figuring out the math and writing the code.

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    Default Re: Creating closed figures?

    look at your Least Squares ajustment factors, or employ
    Crandals rule for boundary closures.

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    AUGI Addict sinc's Avatar
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    Default Re: Creating closed figures?

    As best I can tell from the ACAD documentation, those are for adjusting traverses - i.e., entering occupied points and measured angles/distances into a traverse loop and adjusting that. I'm not trying to do a traverse closure. I'm trying to recreate a figure (usually one someone else has drawn in AutoCAD) to a given specification (the legal description). Maybe creating a "best fit" closed figure is a good way of describing what I want to do.

    In other words, someone else has drawn a closed figure in AutoCAD, and labelled its sides with bearings and distances rounded to the nearest second and .01 feet. All I have is a paper printout of this labelled drawing, and need to recreate this drawing in AutoCAD. If I just draw the figure using the labelled distances, I get closure error, and can't create a closed figure (for areas, etc.). Therefore, I need to close the figure. However, I don't want to do something like simply chamfer the gap closed - that changes the lengths of the two sides, so if I now label the figure with the autolabel commands, the courses in the resulting drawing are not the same as in the original drawing. A mapcheck will also contain courses that do not match the original legal description. In order to draw a closed figure and still have the autolabel, mapcheck, etc. work, I have to manually tweek each course until I can get the figure closed, but changing each course by little enough so that after rounding, it is identical to that in the original legal. Since the original legal was frequently created using AutoCAD (or via other methods, but with enough precision not to make a difference), this is usually possible, if sometimes time-consuming.

    Closing the figure has another impact as well - I frequently end up piecing adjacent parcels of land together. If I just chamfer off a corner (essentially leaving all the closure error in one place), this can end up making it difficult to piece the parcels together.

    I do this a lot, and although I've discovered the Delta option of the Lengthen command makes it go relatively quickly, it's still a pain, and can involve a lot of repetitive work.

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    AUGI Addict sinc's Avatar
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    Default Re: Creating closed figures?

    It occurs to me that I could probably write a Lisp routine that would allow me to select a polyline as input, use the polyline data to generate a traverse loop, adjust the loop using the Crandall rule, and draw a new polyline using the adjusted traverse loop. That would probably accomplish what I want with minimal headache.

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