reducing number of segments in polylines

[MrBrady]

we recently hired out to new company to acquire topographic information on a 8000+ acre site ... some sort of new laser acquisition system .. "LiDar" or something ..... I am using the polylines in there file, or at least trying to .... miles of polylines, each containing 10's-100's of thousands of line segments .... I can not work with this, is there a an existing command \ lisp that reduces the number of line segments in a polyline... say, skips or deletes every other one

 

[lpseifert]

Try here:

http://new.cadalyst.com/code/tips/CodeSearch_Detail.cfm?ID=1477

or:

http://www.4d-technologies.com/geotools/manual/cleanup_tools.htm

____________________
Acad2006, Terramodel

 

[MrBrady]

the tip1477 does not seem to work .... it will not accept polylines as a selection, ... "0 found"

also on this forum was an older topic (with the term "weeding" i could find it) a tip2171 that would not work right either

i did a search for other "weeding" lsp's, found a few, but they do not work in other ways .. most are for R13

I am using AutoCAD 2006, with EaglePoint,

lay some knowledge on me

 

[CarlB]

Seems that most weeding routines you can find are for "heavyweight" not "lightweight" polylines.

That's probably why tip1477 didn't accept your polylines.

Try the one at

http://www.autocadeverything.com/help/lisp-routines/1706-polyline-smoothing-lisp.html

 

[chicopee]

I am not sure if this is what you are looking for, do a PEDIT command on one of the polylines and then select the option FIT. The segmented polyline will then smooth out to give you a curved polyline.
This is the way to contour a plot plan. Elevation lines should be smooth and not be of the form with discreete straight lines.

 

[MrBrady]

I thank you all for your help

the tip 1706 seems to get the job done, its slow but works, I found a few polylines that it will not select, with the "light" vs "heavy" in mind Ii used the 1477 and it worked on them; a little more to my liking in fact...

I do not know the deference between heavyweight" and "lightweight" polylines, can I convert them, is there an advantage one way or the other

your right chicopee, I always smooth out my contours; but doing so did not seem to reduce file size. blocking them did help, but until I like the contours flow, I will have to manipulate them a bit, these contouring programs may be technically accurate, but the "tin" seems to reach a little too far. File size is my main concern; a 170mb dwg(after purge) is proving a little hard to navigate. (and thats just the contours to be x-ref into another dwg. after that, smooth it is.

 

[CarlB]

A "heavyweight" polyline is a regular polyline entity. All polylines were of this type through R12 or so. A "lightweight" polyline (identified as a "lwpolyline") was introduced to take up less file/data storage size, for 2D polylines. You can use the command CONVERT to change selected polylines from one type to the other. The system variale PLINETYPE controls what type is created.

 

[gpavlab]

Just something that I thought you would interesting.
LiDAR is synonomous to Radar- where Radar is an acronym for Radio Detection And Ranging. LiDAR stands for Light Detection And Ranging since LiDAR uses lasers (light wavelength) and Radar uses radio waves.

 

[lpseifert]

About 6 years ago I was involved in a gas pipeline project that used LiDAR for gathering the topographic data for a gas line's corridor. We found that whenever the corridor crossed treelines, barns, fences etc., the elevations would jump 4, 10, 30, 60' (as seen on aerial photos). It seems that LiDAR couldn't distinguish between ground surface and trees, roofs, bushes, birds, etc. What a headache to try and filter out the erroneous points. I hope the technology has advanced since then.

____________________
Acad2006, Terramodel

 

[MrBrady]

I am not sure what the history is, but based on this one project and the few lines we cut, the LiDAR data seems to right on. I have gotten way to much data to use in fact; a topo grid of about 0.3'. every little dip and mound, a slight mound around every tree, we can even see some debris, even the two eagle nests (size location, and how high in the tree they are). as a surveyor\engineer, I don’t think I am ready for this degree of accuracy. it has taken a lot of time just to decide what not to use (a lot). However, still considerably less time to do topo a 8000+ acre site conventionally (too many trees to go GPS) on a side note, i was actually hopeing that tree's came with it; they did'nt, at least not in this case, just elevations

 

[chicopee]

I dont know if this is too late-- one way I reduce file size is to make the drawing into a Wblock, then I open a new drawing and insert the wblock exploded. Many handles are eliminated and file size is reduced and on many occassion substantially.

 

[PeterCharles]

Is your starting point data an ACAD DWG file or an DXF file?
If it's a DXF file then it's a plain text file and you can write a programme (VB or anything that can manipulate text files) to identify the vertex points in the polyline and reduce them a a smaller number.

 

[MrBrady]

My Base is ACAD, and i am blocking in the contours from the LiDar .dwg .... i am not using there points, far too many. Right now the contours are all that exist in this dwg, i have yet to block it into my base

the lisps given here seem to work, just not reliably. I am having one of my guys look into another program "boss" or something, it has weeding built in, along with alot of other stuff we would find useful