Create a continuous boundary using intersecting polylines

[jmorrison2Q85R]

Greetings, I think I've run into the dreaded Hatch Boundary and Boundary Command unreliability issue so I'm hoping some one can suggest an alternative for what I'm trying to do.

This is a basic construction site plan and I need to apply offsets to various imported data.

1) A GIS contractor generates a DWG file with wetlands data.  The wetlands are often 3D polylines.  I flatten these using MAPCLEAN.

2) I apply an offset to the wetlands plines and draw an arbitrary closed pline around the area I'm interested in.

3) I want to use the BOUNDARY command to create a new pline at the maximum extents of the overlapping offsets.  This kinda works sometimes, but most of the time, it behaves unpredictably.  In this example, it finds the closed circular areas but not the (also closed) long skinny area.  

I have also tried using HATCH.  The preview looks almost perfect, but then you click and it basically acts just like BOUNDARY.  (See below, preview, then finished hatch.)

I have copied this section out into a smaller DWG attached to this post.  The smaller file behaves the same way.  All plines are closed and non-overlapping.  Is there something I'm missing in the HATCH or BOUNDARY commands or is there another way I should be going about this?

[O_Eckmann]

Hi,

You have to be very carful with boundary command because it reacts according level of zoom.

Here is a screen cast with your data, 1st attempt with zoom on entire window, and 2nd attempt with a very big level of zoom. In 2nd case, it's OK.

To avoid such problem, best solution is to create REGION of each closed polyline, and create an UNION of these REGION, then EXPLODE resulting REGION and MAPCLEAN to recreate enclosed polylines.

Olivier

[parkr4st]

IMHO far easier to use a sdf file and buffer the objects

MAPEXPORT the wetland areas to a SDF file as polygons

apply MAPFDOBUFFERCREATE command selecting join all buffers and OK

Feature overlay analyse with symmetric difference and the result buffer area is that of the buffer area outside the wetlands.

Mapimport if you need cad objects

Dave P

[jmorrison2Q85R]

@O_Eckmann Thank you for your help!  I had read that BOUNDARY was zoom-dependent but I was thinking zooming out would help.  Thank you for showing how that works.  It does seem strange that AutoCAD works this way though.

[jmorrison2Q85R · Accepted solution]

@parkr4st 

Thank you for the tip!  My CAD background is with Solidworks and I've only been working with this type of land-development work for the last 5 months.  I've come across some methods like yours but they are very foreign to me.  What's worse is that my very experienced colleagues also don't seem to use techniques like this.

Can you go into a little more detail on how this works?  I exported the wetlands as an SDF but I get lost at the MAPFDOBUFFERCREATE step because I don't have any FDO layers, and I don't know what those are.  I will continue to research along this line of thinking but if you have time to really spell this out I would much appreciate it!

[jmorrison2Q85R]

UPDATE:

Figured out the FDO layer thing with buffers...very neat.  I'm now working on figuring out the Feature Overlay portion of the technique.

[parkr4st]

Check this site  https://knowledge.autodesk.com/support/autocad-map-3d/learn-explore/caas/CloudHelp/cloudhelp/2018/EN...

overlay analysis  https://knowledge.autodesk.com/support/autocad-map-3d/learn-explore/caas/CloudHelp/cloudhelp/2018/EN...

https://knowledge.autodesk.com/support/autocad-map-3d/learn-explore/caas/CloudHelp/cloudhelp/2018/EN...

overlay analysis answer questions.  For my example the question is "What portion of the buffer is not wetlands?" 

Answered by the symmetric difference analysis of the wetlands and buffer FDO layers

[jmorrison2Q85R]

@parkr4st 

Thank you again.  Here's how I ended up getting this to work.

1) MAPEXPORT Wetlands Layers to SDF

2) Create SDF connection --> add to map

3) MAPFDOBUFFERCREATE based on SDF of Wetlands

4) MAPIMPORT (as closed polylines) the SDF of the buffer onto layer 0

5) Selected exterior polylines (very quick) --> moved to setback layer --> froze all layers except 0 --> quickly select and delete interior plines.

This is awesome, I really need to learn more about the Map3D toolset.

One question left:

Our team plays pretty fast and loose with coordinate systems, which seems like a bad idea but what do I know?  The way I understand it, our GIS contractor gathers the data and exports it as a DWG.  This DWG file has drawing units of feet but the features are actually scaled in meters.  No coordinate system data is imbedded in the DWG.  This DWG is then copy/pasted into our DWG template and the objects scaled from meters to feet.  Using GEO, the location and coordinate system are established.  We choose the coordinate system based on nothing really, just something near the top of the list, often a HARN system or NAD83.  This has worked well enough in the past.

Now that I'm playing with these more powerful tools, I ran into a problem.  My drawing was in HARN/17.UTM-17 which is meters based.  Everything goes fine until I run the MAPFDOBUFFERCREATE.  I enter my buffer as 30 and select feet from the drop-down.  The buffer that is created is 9.144 ft.  So it appears that the MAPFDOBUFFERCREATE command is seeing 30 ft, converting that to 9.144 meters, then applying that as 9.144 drawing units which are feet.

I tried converting the drawing to a foot-based coordinate system and redoing everything but the MAPFDOBUFFERCREATE failed with an error message about coordinate system translation exception. (?)  SO my workaround was to go back to the original and just enter the buffer as 30 meters and everything worked great.

...so much to learn.

[АлексЮстасу]

1. AutoCAD have problems with Hatch and Boundary.
2. For Hatch, you can use the "Select objects" mode:

Pick internal point or [Select objects/Undo/seTtings]: S

[АлексЮстасу]

The best thing to solve the Boundary problem is TotalBoundary.
See the App Store.