AutoCAD Map 3D General Discussion

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Active Member
coalprpmapper
Posts: 10
Registered: ‎09-02-2004
Message 1 of 10 (329 Views)

negative area mpoly / shp object

329 Views, 9 Replies
07-12-2007 08:04 AM
I export Map 2008 mpolys with object data to shp files. ArcGIS sees some objects in the shp files as negative areas. Tracing back, I found that Map is generating random negative-area mpolys from closed polylines. Doesn't matter whether or not the original polyline is digitized in clockwise or counterclockwise direction, contains doughnut holes or not, or has object data attached or not. Also, at random I’ve selected negative mpolys, gone back to its original file and its original unaltered polyline, regenerated mpoly and now it’s not negative. Question 1, why negative areas?

I can get rid of the mpoly negative area using “MapMPedit” Rebalance, but it’s a pain when several hundred mpolys have negative areas. However, after I rebalanced all the negative mpolys and exported a shp file, ArcGIS now sees ALL the objects as negative area. Question 2, anybody seen this, and any workaround?
Distinguished Contributor
auroramatt
Posts: 163
Registered: ‎06-09-2006
Message 2 of 10 (329 Views)

Re: negative area mpoly / shp object

07-12-2007 08:37 AM in reply to: coalprpmapper
Have you opened it in the task pane through Autocad Map 2008? Autodesk is really weird with numbers. I think they have some major problems because I will use the annotation template to display a number like 40.1 and it will turn it into 40.00000000000000000098 when I display it. Never entered it that way but that's how it gets displayed. I wish I had a copy of ArcGIS ;(
Active Member
coalprpmapper
Posts: 10
Registered: ‎09-02-2004
Message 3 of 10 (329 Views)

Re: negative area mpoly / shp object

07-12-2007 09:46 AM in reply to: coalprpmapper
I haven't tried the task pane. I deal only with the Map side, doing property mapping. My company uses AutoCAD to design / operate dozens of mining operations.

The main reason I use Map is to be able to feed the 3 ArcGIS users down the hall so they can do their interactive web site and run specialized studies / queries. We'd go completely with ArcGIS for our property control, but the GIS people can't figure out how to quickly feed the multitude of AutoCAD users with stuff they can use without jumping through a lot of hoops. I know nothing about how this impacts them, but the GIS people get nervous about negative areas, and frankly, I don't like it either.
Active Contributor
jnovak
Posts: 48
Registered: ‎08-27-2003
Message 4 of 10 (329 Views)

Re: negative area mpoly / shp object

11-01-2007 08:01 AM in reply to: coalprpmapper
I just ran into this today. I imported a shapefile and some of the resulting mpolygons have negative areas. This makes querying the areas pretty exciting. Anyone figure anything out for this?

Thanks,

-Jeff
Active Contributor
jnovak
Posts: 48
Registered: ‎08-27-2003
Message 5 of 10 (329 Views)

Re: negative area mpoly / shp object

11-01-2007 08:17 AM in reply to: coalprpmapper
Oh, OK. So if I import the shapefiles into AutoCAD 2006 then none of the mpolyons have negative areas.

Everyday I am thankful that I have not yet uninstalled 2006...
Distinguished Contributor
cadman009
Posts: 336
Registered: ‎12-17-2003
Message 6 of 10 (329 Views)

Re: negative area mpoly / shp object

01-07-2008 01:37 PM in reply to: coalprpmapper
I'm having the same problem with Land Desktop 2008. Any solutions yet? I was hopeing Land Desktop SP2 had solved it, but it's still happening. (I was advised a while back to post here since this appears to be a Map problem.)
Active Contributor
jnovak
Posts: 48
Registered: ‎08-27-2003
Message 7 of 10 (329 Views)

Re: negative area mpoly / shp object

01-07-2008 04:06 PM in reply to: coalprpmapper
I haven't found a good way to deal with the negative areas yet. As a work around you can try:

(sqrt (* .AREA .AREA))
Distinguished Contributor
cadman009
Posts: 336
Registered: ‎12-17-2003
Message 8 of 10 (329 Views)

Re: negative area mpoly / shp object

01-08-2008 06:46 AM in reply to: coalprpmapper
Thanks. I'm wanting to use the shapes in ArcGIS though and the negative areas cause some wierd behavior. I read on an earlier post that mapexport4 will work, but I tried it and it hangs up and doesn't create a shape. This is crazy! Importing and exporting shapes to and from ArcGIS is the main thing I need to do with Map! Any GIS users out there know how to fix the polygons from AutoCAD Map that read as negative areas?
*Tripp Corbin
Message 9 of 10 (329 Views)

Re: negative area mpoly / shp object

01-08-2008 07:11 AM in reply to: coalprpmapper
Depends on how your DWG is set up and what you need on the ArcGIS side. If
you do not have object data and all you need to do is import the stick work
into ArcGIS, then just bring the drawing into ArcGIS and export as needed.
ArcGIS with the latest service packs will read the latest DWG format.

If you do need the object data there are a couple of things you could try.
Try exporting to a coverage and then bring that into ArcGIS. If you are
dealing with polygons try transferring the OD to a centroid. Then export the
centroids to a point shapefile. Next bring the drawing into ArcGIS and use
the construct features tools to generate polygons. lastly do a spatial join
to transfer the OB back to the polygons.

--
Tripp Corbin, MCP, CFM, GISP
Vice President, GIS/Mapping
ESRI Authorized Instructor
Keck & Wood, Inc.
www.keckwood.com
(678) 417-4013
(678) 417-8785 fax

Keck & Wood, Inc offers a range of GIS services and training. Please visit
www.keckwood.com for more information including a schedule of upcoming
classes.

wrote in message news:5814838@discussion.autodesk.com...
Thanks. I'm wanting to use the shapes in ArcGIS though and the negative
areas cause some wierd behavior. I read on an earlier post that mapexport4
will work, but I tried it and it hangs up and doesn't create a shape. This
is crazy! Importing and exporting shapes to and from ArcGIS is the main
thing I need to do with Map! Any GIS users out there know how to fix the
polygons from AutoCAD Map that read as negative areas?
New Member
zoetermeer
Posts: 1
Registered: ‎08-21-2008
Message 10 of 10 (329 Views)

Re: negative area mpoly / shp object

08-21-2008 03:30 AM in reply to: coalprpmapper
I have the same negative areas within Autocad Map 2008. I don't export anything.
De MPolygons are converted from polylines and with Edit Polygon I added the boundaries of islands/holes which resulted in a nice polygon with a positive area.
However if I did this for another polygon and moved this polygon. Then UNDO'ed this until it was at its orginal place, then the area would be negative.
I checked the inner/outer boundaries and supprise the outerboundary was now an inner boundary and that's why the area is negative. When I changed the wrong inner boundary to outer boundary the area was positve again.
I don't know what the cause is of this fault, but I can redo it with the UNDO command.
The same applies to when I copy the mpolygons and paste them into a new drawing - all area's are negative.
As a workaround I checked my complete drawing with quickselect on mpolygons with areas less than 0, rebalance it and Bob's your uncle. I'm looking for a way to do this automatically, thus select all negative mpolygons and rebalance all.
So anybody?

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