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This 33 minute lesson provides additional techniques for drafting boundary lines from a property survey. In this lesson, we use as a case study a survey document provided by Best Practices Course member Dale Paegelow, an architect in upstate New York.
This survey has multiple curved boundary segments defined in a different way than in the earlier lesson on this topic. The curves are defined by a radius and the subtended angle (the slice of the pie, so to speak). The length is calculated as the perimeter measured along the arc itself rather than the chord length, and there is no bearing angle specified for the chord.
Two of the sides of the property are defined by traditional metes and bounds with distances and bearings indicated in a series of straight segments.
Along each of the other two sides of the property, there are two intersecting boundary curves, one with the convex side facing in towards the property and the other facing away. The center-point of the arc is in each case defined by a radius distance (as written on the survey) along the adjacent property line (which is a straight segment with a standard bearing angle), either along the direction of that property line or going away from that property line but maintaining the same bearing.
The basic approach is to draft each of the two sides with straight segments, then to create the arc boundaries defined at the ends. The set of straight lines on one side along with the two attached arc boundaries are then moved into position, snapping the end of one arc boundary to the end of the matching arc boundary of the other side of the property. When done properly, the opposite side arc boundaries will then close within the standard level of tolerance.
In this case study, the survey was provided to me as two PDF files, each representing a part of the survey document as scanned by Mr. Paegelow. I combined the two in Photoshop to create a single composite that was then resaved as a PDF to be imported into ArchiCAD.
In ArchiCAD, I created a new independent worksheet, then set the scale to match the survey drawing. I then placed the survey PDF, and quickly rescaled it to proper size.
I drew one property line using the bearing angle indicated on the survey. Since the North angle in the ArchiCAD project was set at the original default 90 degrees (straight “up”) it did not match the North angle from the survey document. To coordinate these, I rotated the survey PDF to match the property line with my drafted line, then noted the rotation angle of the PDF. I then adjusted the North angle in the Options menu > Project Preferences > Levels and Project North to match the unrotated survey, and verified that it matched by placing a North Arrow object from the standard library that was set to “Follow Project North.”
NOTE: In ArchiCAD 12 and earlier, to adjust the North Angle for the project, use the View menu > 3D View Mode > 3D Projection Settings > More Sun… dialog.
As part of the process, I defined a custom, very thick pen to use for the property lines so that they stood out easily on top of the scanned PDF survey. I made a visual differentiation between the actual boundaries in this thick red pen and the construction lines I created to locate the arc centers (which were done with a dashed blue pen).
IMPORTANT NOTE: To work properly with survey bearing angles, make sure that the Options menu > Work Environment > Tracker and Coordinate Input checkboxes for “Use relative angle measures” and “Use angle relative to the active Guide Line” are NOT checked. In ArchiCAD 15, this is automatically turned off by ArchiCAD whenever surveyor’s units are chosen; in ArchiCAD 14 and earlier, this must be done manually by the user.
The process of drafting the boundary lines generally follows the methods shown in previous lessons. The main exception is the requirement to draft the arc boundaries based on a center-point defined by the distance along the adjacent straight property boundary line; also, there is the extra step of moving one entire side into proper relationship to the other side.
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