Contour splines don't create the terrain I expect

[ADallas]

Clearly, I'm not thinking about this correctly.

1. On a new plan, create a default terrain perimeter.
2. I drew 8 elevation splines, careful to start and end them outside the terrain perimeter.
3. I opened each spline in turn and set the elevation to 92', 94', 96'...up to 106' in the upper right. Zooming in, the splines are labeled, showing that the lines are around 100'. Each spline started at the default elevation 0', but I manually set other values. There are no other objects on the plan that could suggest anything but 92' to 106'. I checked--Terrain Perimeters don't have an elevation.

  

 

So, imagine my surprise when I built the terrain and got this:

    

This can only be caused by my utter misunderstanding of how elevation splines are meant to translate to contour lines. Help!

 

Alastair Dallas

I'm running Chief X13, Build 23.3.0.81x64 on a Dell running Windows 10.

[Chopsaw]

Sounds like you did everything correctly.  You might want to try it again or post the plan file.  There must be some sort of hidden data.

[glennw]

First off, I would turn off the display of contour lines in layer display options and then have a look for any rouge elevation data.

[Kbird1]

At least one line is still at 0' , (pretty sure I see 0' in your last pic ) , this would cause the "Valley" in the middle...

 

RED numbers means a negative Elevation too.

 

Mick. 

[ADallas]

Here's the actual plan file, as Chopsaw suggested. It is nothing more than an imported surveyor's DWG file. For some reason, Build Terrain invents a pit and two peaks. 

These are the two imported layers: TE-CONT-MAJR (blue) and TE-CONT-MINR (green). I told the import wizard to map both of them to elevation data. The problem is along the middle right--it's a cliff from ~262' to ~272'. There's no depression, nor are there peaks, but Build Terrain adds them:

Following glennw's suggestion, when I turn off the layers for my imported contours (TE-CONT-MAJR, TE-CONT-MINR) as well as the Terrain, Primary Contours and Terrain, Secondary Contours, there is nothing to show. The Layer dialog shows that Terrain, Elevation Data is not used. It should be a 10' cliff from two roughly level building pads, but Chief adds unnecessary drama:

Notice that it does the right thing in the contour-free lower left--it just continues the slope. The surveyor interrupted the contour lines for his elevation labels, but that doesn't faze Chief. Likewise, the upper left looks right--it's roughly level. Where did the pit and the peaks come from? And how can I get rid of them?

 

TH-4th import.plan

[Renerabbitt]

17 minutes ago, ADallas said:

but Chief adds unnecessary drama:

Chief interpolates from the data that you have provided. So Chief, with a lack of info, can only presume that your contour lines continue in the path that you have designated. It has no way of knowing what is flat or peaked without you providing such data. A simple set of extra terrain contours would solve any issues you have.

[Kbird1]

40 minutes ago, ADallas said:

It is nothing more than an imported surveyor's DWG file. For some reason, Build Terrain invents a pit and two peaks. 

 

Now you're changing the story  

 

Many Surveys do not show what is there "today" , the one on record could be from before any work was done or even the 1st Building built,

so there could be many changes, unless you know the Survey is "new" of course, but the Surveyor could of also screwed up the Elev. Data as well.

 

M.

[ADallas]

Kbird1: The DWG file could well contain messed up elevation data, but it is recent. When I had trouble with the import, I reproduced it without importing and posted here. 

 

My question is: How can I tell that imported (or manually-entered) elevation data is going to mess up Build Terrain? If I could see the erroneous data, I could correct or delete it before clicking Build Terrain. Alternatively, is there any way to edit the result of Build Terrain to fill in the pit and sand down the peaks? I can add more elevation data, but what are the rules?

[ADallas]

35 minutes ago, Renerabbitt said:

Chief interpolates from the data that you have provided. So Chief, with a lack of info, can only presume that your contour lines continue in the path that you have designated. It has no way of knowing what is flat or peaked without you providing such data. A simple set of extra terrain contours would solve any issues you have.

Thanks for replying, but that makes no sense to me--I posted here what I provided, and it shows no peaks or pits. They came out of nothing.

 

I'll try adding extra terrain contours, but it's not "simple"--should I use points, lines, splines? Is it okay to cross contour lines?

[ADallas]

For the record, this was discussed here 15 months ago: 

 

[Kbird1]

18 minutes ago, ADallas said:

I reproduced it without importing and posted here. 

 

You didn't post your reproduced plan or I would of looked at it , just pics....

it appeared to have 1 spline still at 0'  but I'll check back tonight

 

M.

[Renerabbitt]

20 minutes ago, ADallas said:

Thanks for replying, but that makes no sense to me--I posted here what I provided, and it shows no peaks or pits. They came out of nothing.

They came from interpolation of the data provided as well as the lack of data.

[ADallas]

Thanks, everyone, for your help. I think I have a handle on it now--I can provide additional elevation data, as @Renerabbitt suggested. I blasted some flat regions on top of the pit and the peaks and also turned down the granularity in the Terrain Specification (Low seems to work). @Kbird1, thanks for looking, but I was careful to check each spline's elevation.

 

Thank you, also, @Renerabbitt, for your interpolation diagram. I can almost see what confused the algorithm. (But I'm still confused.) I think I'll follow @DavidJPotter's advice from 15 months ago and import the survey data as lines that I can trace myself. When in doubt, do it yourself.

[glennw]

2 hours ago, ADallas said:

I'll try adding extra terrain contours, but it's not "simple"--should I use points, lines, splines? Is it okay to cross contour lines?

Don't use points - too hard to keep track of.

Use lines, splines or elevation regions.

Try and avoid the use of terrain modifiers

Do not cross contour (Elevation) lines.

Always best to trace the imported data with Elevation Lines or Elevation Splines when practical.

Best to avoid breaking elevation lines for text or other data like heights, etc.