Topic: ( C3D ) Accumulation errors

[Mark]

How do you guys deal with accumulation errors in C3D?

One of my drawings just went down in flames .... over 0.01'. The stations didn't match the inverse distance on my alignment. I'm guessing it's round-off.

[Dinosaur]

I haven't tried this but can you set up a label style that truncates the rounding rather than round normal and give that style to the questionable course?  It would have to be done in the label component editor per yesterday's problem.

[Mark]

I'll try tomorrow Dino. I had to explode the stations and renumber them to get it out the door today.

[Mark]

The problem with this alignment was if you added up the total distance using the stations it wasn't the same as the total distance shown by the inverse labels. So C3D is taking the total distance then rounding the numbers. /guess

[CADaver]

Plan distances or TRUE distances??

[Dinosaur]

Plan distances or TRUE distances??

They would be the real distances - it is just an accumulation of the program rounding one direction than the other.  Civil 3D , like its grandpa Land Desktop, is quit anal about the intermediate course distances being rounded with  exactly the same precision as the overall distance and the nature of an overall design dictates that it is more important that ends of a course fall exactly at an intersection or it runs exactly parallel with or perpendicular to something rather than measure an exact distance or bearing.  This means it is common for a course that says it is 123.45 feet to be actually be 123.4549 feet or 123.4451 feet.  All it takes is for two runs at either extreme to have the sum of the courses be more than the precision level allows and the overall length will show as being 0.01 foot different.  That less than 1/8 inch drives reviewers bat-squack and once found, the design is flagged as inaccurate due to rounding and kicked back for non compliance.  If this is in a critical area that has been designed at minimums, the correction may force slopes for streets or pipes outside of allowable range or cause a lot to not meet area requirements or not close with the required precision.

[CADaver]

That less than 1/8 inch drives reviewers bat-squack and once found, the design is flagged as inaccurate due to rounding and kicked back for non compliance.  If this is in a critical area that has been designed at minimums, the correction may force slopes for streets or pipes outside of allowable range or cause a lot to not meet area requirements or not close with the required precision.

Somebody needs smacked with a common sense stick.  How'd they do it thirty years ago??

[Dinosaur]

Somebody needs smacked with a common sense stick.  How'd they do it thirty years ago??

with their K&E jewel points on the vellum by hand.  They could make the numbers work.  A Civil 3D label is part of the object itself and as yet, can not have its value over ridden.  You can explode the label and the resulting block and lose all associativity or you can find a way to trick the program to display the numbers you want - like the truncating option I told Mark about which is best if it will work.  He can also shorten or lengthen his alignment just enough to make the overall number match the sums - a problem if he shortens it and he is going to an intersection because he just lost his intersection.

[Jeff_M]

It took some doing, but I think I finally have convinced the main architect we work with to quit giving us houses that are XX'- 4" (or 8") wide. They have agreed to go with 0", 3" 6", or 9" because 10 lots 45.33' wide adds up to 453.30' but the overall dimension will always come up 453.33'. Yes, it can be fudged, but everyone's life is easier if you eliminate the potential problem.

[Jeff_M]

What I've done is create Label styles that use Expressions. The Expression formula is merely {Segment Length} - 0.01.  The label itself I set to color RED so it stands out from the regular labels and I can quickly tell which labels have been altered. This way, when linework changes I can reset the label to a normal label and check for the accumulation error again.

[Mark]

I haven't tried this but can you set up a label style that truncates the rounding rather than round normal and give that style to the questionable course?  It would have to be done in the label component editor per yesterday's problem.

Truncating the Geometry Point label almost worked.

[Mark]

That less than 1/8 inch drives reviewers bat-squack and once found, the design is flagged as inaccurate due to rounding and kicked back for non compliance.  If this is in a critical area that has been designed at minimums, the correction may force slopes for streets or pipes outside of allowable range or cause a lot to not meet area requirements or not close with the required precision.

Somebody needs smacked with a common sense stick.  How'd they do it thirty years ago??

Like I did it yesterday .... by hand! Of course I might as well be using vanilla ACAD if we have to keep labeling every thing by hand.

[Dinosaur]

Jeff probably had the best suggestion unless tweaking the endpoint of your alignment won't cause you problems.

[CADaver]

That less than 1/8 inch drives reviewers bat-squack and once found, the design is flagged as inaccurate due to rounding and kicked back for non compliance.  If this is in a critical area that has been designed at minimums, the correction may force slopes for streets or pipes outside of allowable range or cause a lot to not meet area requirements or not close with the required precision.

Somebody needs smacked with a common sense stick.  How'd they do it thirty years ago??

Like I did it yesterday .... by hand! Of course I might as well be using vanilla ACAD if we have to keep labeling every thing by hand.

I guess my point was the numbers were the very same (round-off and all) but no one had a canary over and 1/8" on an alignment.  The surveyors won't get it that close three times in a row over any real distance.

Can you change to three decimal places instead of two?

[Mark]

Jeff probably had the best suggestion unless tweaking the endpoint of your alignment won't cause you problems.

Only you can't edit individual geometry points on an alignment, that I know of anyway. I could tweak the endpoint but then the geometry in the dwg would be wrong, which will likely mean more to the person that receives it.