DTM from Photogrammetry

I am trying to create a DTM from breaklines and points supplied by a
photogrammetrist. I realize many of the inherent shortcomings to the
process but I'm having a few problems with the product delivered from
the photogrammetrist.
A little background. 1) I don't know what type of stereoplotter the
photogrammetrist is using. 2) All line work is being generated using
Microstation 3) The project elevation ranges from 0m elevation to 80m
elevation.
4)All breaklines are supposed to be delivered as 3d polylines
Here are the problems
1) There are breaklines that are coming in at ridiculous elevations
(ex.2400+ and -1300+)
2) There are a lot of breaklines that are 2d polylines
3) Many breaklines, especially at headwalls, are not being utilized by
Autocad in the tin creation. I realize that vertical walls cannot be
efficiently utilized, but these aren't being used at all.
If anyone has any input as to either how these errors are being
generated by the photogrammetrist or solutions....it will be greatly
appreciated.Also- if anyone knows of a more appropriate group for this
question- let me know.
Thanks- Tom
Reply to
tom
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I'll skip trying to sell you software and try helping you. ;)
You might want to post to the Land Development group on Adesk's site. (I'm assuming you're using that since you didn't mention other applications.)
I've done this a few times before and don't see what their equipment has to do with it. One company used to send us 'breakline' files, that were basically a coordinate file with a 0/1 indicator for new/continue line. I wrote a lisp to import them.
What type of product are you trying to end up with, a contour map, a 3D model, etc.?
Reply to
TomD
Thanks for the direct approach! As far as an end product- a 3d model will be my end product. Traditionally, we specify that breaklines delivered will be 3d polylines. 2d polylines and even polylines w/elevations would be acceptable...but here's the situation: There are breaklines along a feature that are 3d polylines w/real world elevations at the vertices. But... in some places these lines are only either "lines" or 2d polylines (with outrageous elevations) When I use the Autocad command to list the lines, correct elevations are reported. When I use the LDD command to list the properties of the line, an erroneous elevation is reported (in the range of hundreds of thousands of meters). This is also what is actually being modeled...huge spikes in the surface. Another photogrammetrist suggested that this happens when performing 2d edits in Microstation. I can manually edit the breaklines, but this would be better performed by the photogrammetrist whom doesn't see any problem. So.... any ideas? Thanks again
Reply to
tom
Are you sure there aren't POINT objects (or anything else) being picked up by LDD with the erroneous elevations? Sounds quite peculiar to me. Are these actual LINE/POLYLINE objects as opposed to some type of ARX objects? I'd think one of these two scenarios is happening to you.
I'd be happy to take a look at a SMALL sample of such things if you'd like to email me something. (If you do, please keep it under 100k.) I can try modeling with EaglePoint and let you know what kind of resutlts I get.
Reply to
TomD
I've been training for a few days. As mentioned earlier, all lines are either 2d polylines or generic lines. Both have the same problem though. Using vanilla cad to list the properties, the correst z value is reported. Using the LDD properties command, the erroneous z value is reported. All points have been converted to civil point objects, the drawing has been audited,and the breaklines were declared seperately than the points when building the model.I'm hoping to meet with the photogrammetrist to sort it all out. I'll look into the ARX (I really don't think that's the case). I'm thinking that the lines were created in two or three vertices intervals and then later joined (due to limited visibility through the canopy). For some reason, it appears that lines with less than four vertices tend to report erroneous z values....Has anyone else seen this or know why. This is not the first time that I've received breaklines from a MicroStation user and had this problem. Thanks- Tom
Reply to
tom

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