depending on what your aerial topo company provides, they sometimes include
a drawing that contains points and softbreaklines with is a much better way
to build a surface, of course, than from contours. Check your deliverables
and see if there isn't some sort of non-contour drawing in the package and
build a surface from that.
It depends what part of the country you are in and how much your aerial topo
company understands what you need.
I personally have not had success getting the actual TIN from aerial topo
companies, because I have been told that isn't how they get their contours
(at least the ones I work with).
I guess when it comes to what Laurie refers to as "C" or "D" class models-
it really depends on what exactly you are trying to accomplish.
Recently I worked on a large river project. Building a TIN from the
delivered aerial topo would have meant that my sections would show grade
changes every half foot or so. When you are dealing with 1000 ft or more
cross sections, that kind of detail is really just not necessary (At least
not for what we were working on)
It is up to you to decide how much you are willing to lose for the sake of
drawing performance.
Another thing that can slow you down- once you build the surface, remove
your heavy polyline contours out of the drawing. That helps a lot. But
make sure you make your surface so that removing the polylines doesn't
degrade the surface. I am paranoid, so I do a LandXML export-reimport, but
I have heard snapshots will do it, too.
Dana
--
Dana Breig Probert
http://civil3drocks.blogspot.com/
http://groups.yahoo.com/group/cadapult_civil
"Laurie Comerford" wrote in message
news:5179968@discussion.autodesk.com...
Hi,
Why didn't you get the DTM from the survey company?
They've build a DTM, then given you a "B" class repesentation of it. I
presume in a drawing file - you still haven't said so. Now you are
suffering hell/delays etc. because you can't even get a "C" class model from
the supplied data.
Do you design all the roads similtaneously? If you take that approach then
you might need all the model at once, but otherwise why not create a series
of DTMs, each covering sufficient area to allow manageable portions of your
job to be designed.
No matter how you approach it with a drawing size in the 50Mb plus area you
will get crashes, slow work and suffer far more than you would be breaking
your project into pieces you can work on
Dana has suggested you use the Map cleanup process on the contours, before
attempting to build your DTM.
This will reduce the quality of the data and if done injudiciously might get
you back to a "D" class model.
I would go back to teh Survey company and get a DTM from them - preferably
as 3Dfaces.
The I would define a series of outlines of DTMs you need to work with and
use Map queries to import the 3Dfaces for each into separate drawings and
build DTMs in each of these from the 3Dfaces.
--
Laurie Comerford
CADApps
www.cadapps.com.au
--
Laurie Comerford
CADApps
www.cadapps.com.au
wrote in message news:5179827@discussion.autodesk.com...
The file we received from the aerial survey company contains only polyline
contours. We have to make a surface from those.
We have to keep it as one surface because we are designing roads that
traverse the whole property.