Jump to content
Sign in to follow this  
jnr

DTM file size out of control

Recommended Posts

So I have a 3D polygon site model source file that is around 1.7 mb in size. When I give them a Z dimension and then build a DTM, the file balloons to 100.7 mb in size and frankly, becomes unruly. The 3d polys are converted from 2D polys (with as few control points as possible) and drawn natively in 2013.

Any ideas why the file gets so big? All I can see is that going from 2D to 3D converts the contours into bezier curves with a gagillion unnecessary control points.

thoughts?

-J

Share this post


Link to post

jnr, it is not uncommon for Site Models to dramatically increase file size. There is some pretty intense triangulation being performed behind the scenes. One thing you might try is the AEC>Terrain>Simplify 3d Polys command. If used carefully the command will reduce the 3d Poly vertex count and in turn simplify the Site Model triangulations which should reduce the file size. Careful not to over simplify as this may introduce topographic errors*. In my experience Simplify 3d Polys will make the Site Model much more responsive (less unruly). Of course I would suggest trying this on a copy... TIP: Copy, then Paste in Place the original Polys into their own clean Design Layer. That way you will be able to compare to the Simplified ones so that you can determine the optimal (and acceptable) distance between vertices...

*All simplification will introduce some level of error. In reality the data you started with was probably interpolated in the first place, so it was already less than 100% perfect. All of these errors can be additive. You need to determine how much accuracy you really need (and how much accuracy will be transferred to the field).

Share this post


Link to post

Peter:

thanks for the tips. since the project is conceptual in nature and the DTM intended to sell a concept for a bridge and underpass design, all accuracy bets are off!

I'll give the simplification gig a ride and see what happens. Any advice on an acceptable value for the tolerance?

-J

Share this post


Link to post

It depends a great deal on the "regularity" of the topography. If there are no major radical out or in croppings (new word?) then I would try 2-4ft (or more?) between vertices... Heck, just try it and see what happens!

Share this post


Link to post

jnr,

just to chime in...i have found that reducing the amount of geometry going into a dtm greatly reduces the file size and workability of the dtm. for conceptual work i find that a 4' tolerance for 3d polys is adequate. but it depends on the terrain, the scale and level of detail.

going forward...any hardscapes, texture beds, etc. that you add to the dtm may need to be simplified as well. the process is cumulative...everything adds up. i have found myself late in the project having to go back and reduce the amount of geometry (simplifying) in order to keep moving forward. so, save all your 3d data just in case.

cheers,

ray

Share this post


Link to post

guys:

thanks for the advice. I've tried to reduce the geometry in the 2d polys as much as possible before heading into 3D land. I'll try setting tolerance to 4'. Its a 1000' x 1400' urban site. I hope I don't need a Cray computer when its all said and done.

-J

Share this post


Link to post

Peter:

So my understanding is that it is better to reference the DTM into the file as a design viewport. My problem is then that coordinating site modifiers (retaining walls specifically) becomes a hassle as I have to go back to the DTM source file and figure out where to install the walls (references such as adj buildings, sidewalks etc are not in the DTM). Seems that since Vectorworks stores the DTM data in the target file (ie the site w-buildings cars trees bridges etc) anyway, its already bloated and you might as well just paste the DTM in or make it a symbol.

I hope I'm being clear and have the terminology right.

BTW simplify didn't work for the complexity of what I'm doing. I did manage to get it down from 187mb to 130mb and so far its not too unwieldily on my iMac. Not as quick as a sketchup file but a least I can work with it.

-J

Share this post


Link to post

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this  

 

7150 Riverwood Drive, Columbia, Maryland 21046, USA   |   Contact Us:   410-290-5114

 

© 2018 Vectorworks, Inc. All Rights Reserved. Vectorworks, Inc. is part of the Nemetschek Group.

×