How do eliminate certain points/lines from the DTM creation?

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Posts: 15
Joined: Sat Mar 15, 2008 5:54 pm
Location: Mandurah, Western Australia

How do eliminate certain points/lines from the DTM creation?

Post by DonG » Sun Mar 30, 2008 4:36 am

What control do I have over data that is used in the creation of the DTM. It appears that even if I turn off layers that are not required, ( like my control layer which will show crazy elevations ) they still show up in the TIN and then the contour. Sometimes I only want lines for appearance ( like a roof line which overhangs the actual ground wall position ) but want ground elevations of the wall only in the DTM. The layer for "roof line" and "control" still shows up in the calcs.
PS - I think a quick training visit to British Colombia is on the cards!! ( Tax deductible of course ! )


John Gallagher
Posts: 64
Joined: Fri Nov 08, 2002 1:35 pm
Location: Long Island New York

Post by John Gallagher » Sun Mar 30, 2008 2:51 pm

Go to the pull down menu MsPoints-->Active Coordinate Editor.
In the window go to sort by elevation.
Pick the points you want to exclude from the dtm and right click and select the exclude from dtm option.
Another way is to tell whoever is doing the data collection in the field to make sure that the points you want to exclude have very odd elevations (where I survey this means anything over 500 or under minus 500 is not to be seen as a valid input.)
You can also set in the MsModeling drop down menu under configuration settings data extraction the minimum and maximum z values for your tin.
As an example if you know that the area you are surveying in is at elevation 200 or more,you can set the minimum z value at 199 and the program will ignore any elevation at say 150.

Hope this helps,and as Richard noted to a different post of yours ask questions on this forum,we all at one time or another were newbies.
John Gallagher

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Joined: Sun Nov 24, 2002 6:45 am
Location: Temecula, California

Post by ianw2 » Sun Mar 30, 2008 5:29 pm

Great reply, John!

Don: Are you a diver? If so, come to Southern California for your trainning and we'll work in xome world class Southern California diving at Catalina, La Jolla, Laguna, etc.

Or...I'll gladly come to you! Mandurah supposedly has some fine Western Oz diving.

Ian Wilson
Ian Wilson Land Surveying, Inc.
Temecula CA 92591
(951) 684-1044

Posts: 48
Joined: Mon Dec 11, 2006 10:41 am
Location: Manitoulin Island

Post by Gord » Mon Mar 31, 2008 3:53 am

Another way is in the point descriptions. If you have a crew that can keep track of what will be wanted in the end product, start the descriptions with something that will let automap deal with it.
Ie, when working on topos, any tie I take that I don't want in the DTM (top of fire hydrant) I will start the description with ND . Easy to set up automap to leave anything that starts with ND out of the DTM.
As far as control over the DTM, it works good with points but you can't remove a line from the DTM.

Posts: 15
Joined: Sat Mar 15, 2008 5:54 pm
Location: Mandurah, Western Australia

Post by DonG » Mon Mar 31, 2008 4:06 am

All great replies - thanx guys. Well, California sounds pretty good to me!! I can see a window of opportunity about Jan '09 !! Thanks Ian.

Richard Sands
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Joined: Mon Feb 14, 2005 1:10 pm
Location: Tasmania

removing Lines

Post by Richard Sands » Mon Mar 31, 2008 1:41 pm

When you remove points from the DTM it actually strips all breaks so any linework that has been added in way of breaklines is in effect removed.
That doesn't necesarily remove all linework as some may have been used only as surface entity and unless it was added as a breakline then its not removed. (may stand correcting here)
There's a thread somewhere about DTM creation in this Forum.
I always select my points and create a DTM then view the results by way of the TIN or GRID (Also check contours - view, not draw) etc and if it looks OK I then save that surface. Then I add the linework that acts as breaks. If that looks good then I save that surface.
You can copy surfaces and rename them. You can have one 'Points Only' and one 'After Breaks'. A 'points only' surface allows you to go back to that surface and then add linework if things go pearshape.
Other option is to setup modelling to chose from Points, lines etc.
See the Configuration settings - 'Extract configuration'. This allows you to select what entities you want to include for modelling.
These surfaces are not part of the data base so no 'damage' is done to it if you mess up chosing entities that you later want to discard from the model.
Don, if you get stuck on something, give me a ring - you'll find me in the phone book in Tasy.
There's a lot in teh modelling side but its not overly complicated.

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