Site model

[Monique Freese]

Hello

ISSUE ONE

I have input my survey info and ensured the contour lines are recognized as 3D polys, all the levels associated with each contour line is correct.

The site does not have much fall, pretty much dead flat but I would like to show the basic contours on my site plan.

I have used the contours from the Council GIS maps as source data and traced them, and also spot levels supplied by the surveyor - it would be great if the contours were uniformly rising as they would be easier for the program to create the model, but that is not the case.

 

 

I created the site model and in 2D the contours are all skewed.

 

 

I would ideally like it to present the same as the GIS layout.

 

ISSUE TWO

I can't seem to work out how to set the datum or elevation height on my site model so it corresponds to my house levels.

I understand that Z is my height value and I have input the correct contour values and design layer elevational values for the building via stories, how do I get everything to relate to the site model?

 

I have the site model on its own design layer and set the design layer elevation to 0, is this correct? What does the design layer elevation actually relate to? 

The lowest contour I have input is 2.00m and the highest 3.0m as per the GIS map and my house floor level (supported on poles) is 3.72m.

On the site model settings under general the following:

 

 

 

In the object info under site model the Geo Lowest Z is set to 2000 ..... is this correct?

 

ISSUE THREE

When in flyover mode looking at the following:

1. What do the red lines represent? - lowest and highest contour?

2. I have the skirt mode on so what defines the depth of the skirt? - the lowest contour or the datum set at 0 on the site model general settings.....

 

 

I have just gone into the recreate from source data and have found this: 

 

The portion of contour I have circled is not supposed to be there?

The Z values are incorrect, aren't they supposed to relate the the contour values I have input??

 

PLEASE HELP!!

 

[Monique Freese]

Just looked at my GIS Council source data and the contour I have circled is supposed to be there it must have picked up the line somehow from the imported layer when I was tracing???

[Ross Harris]

I'm Auckland based and use the council gis regularly - but only for initial feasibility. The council gis is very ballpark in terms of levels - at worst it's over 1m out compared to a site survey and on one site, the sewer and manholes were 6m away from where the gis put them. My advice is to not use the gis data for resource or building consent design work - get a survey done. Also don't mix surveyors levels with the gis levels - the inaccuracies of the gis with accurate survey levels will skew a site model, hence the odd contours. Take note of the disclaimer you have to agree to - it goes to great lengths to highlight the data is 'informational' and that all liability rests with the user of the data. You are potentially opening yourself up to liability relying on the gis.

 

ISSUE 1: You can download a georeferenced DWG from the gis - this makes initial creation much quicker. The boundary lines are from LINZ, so are accurate, but the contours are ballpark. The contours (depending on the gis dataset available for the area) can be big steps, so you won't get the detail of a site survey. It sounds like you have mixed the babbage spot levels in, which as I mentioned above, will make the site model inaccurate. Paying for a survey is money well spent and very much a get out of jail free card. 

 

ISSUE 2: Model your house FFL on a design layer at 0m elevation and then create a design layer viewport (DLVP) to send the 'house' as a 3d viewport to the site model. That way you can grab the DLVP and position it where you like and it will report the actual vertical height to the FFL in the site layer. My 'house' layers are storey driven, and the site layer is not associated with a story, so I create a viewport with the house layers in the usual way, but send them to the site layer - not a sheet layer.

Your site layer should be set to 0m elevation so that a gis or survey I port will always report the correct levels. 

Elevation benchmarks - I usually use them in control point mode in the annotation space of the viewport (for flexibility) taking the FFL of the DLVP height in the OIP from the site model layer. From memory, I think elevation benchmarks will report the height of a DLVP... Will have to test 🤔

 

ISSUE 3: 

1. The red lines are a cube representing the top and bottom extents of the site model. 

2. The skirt extents are in the site model settings - you can have it go to 0, a set elevation or it can be to the lowest contour of the site model - which is good for sites at 100m elevation for example. Also good to allow the site model to extend if you are doing cuts that go below the exisitng site contours.

Depending on how you have set the contour multipliers in the site model settings, they can be different to the the gis - also the interpolation VW does creating the site model can create contour variations. Also mixing in survey data with the gis data will cause this to go whacky - as noted above.

 

I can't overstate getting a survey done. An accurate model starts with accurate data, and in the worst case, can save you a day in court .. I will turn a job away if the client won't get a survey done. This is even more critical and mandatory in flood zones since the flooding last year.

 

Edited April 2 by Ross Harris

[Monique Freese]

Thanks Ross

Firstly, yes I agree, most projects will require a survey done and that takes the responsibility out of our hands hence getting Babbage out. We needed the minimum F.F.L. set on site so asked if he could take some levels around the building platform.

 

Thanks for your message, great info in there for me to work through.

 

Even when I don't include the spot levels the generated model contours are still not the same as my source information so is causing no end of confusion.

 

The site is basically flat I but wanted to still set up a 3D model view for the client to have a look including a sun study.

 

I have since set up an imaginary site with a steeper gradient to see if I could figure out the levels (which I obviously haven't as yet).

 

I still need to learn about the ins and outs of site modelling so ISSUE 2 is a bit out of my depth at present as I have only just started using the program. I understand the concept of stories and why we use them but still don't understand why we cant use a datum or set point where the site model can relate to the finished floor level from the design layer.

I am using stories and set my proposed F.F.L to the R.L of 3.72, which is the minimum requirement from the flood report, I can't see why this would not work with the contours set on the site model. I can basically grasp that the site model does not have an elevation as such(???) but need to understand how these CAN work together.

 

I have now become a Pro Member so I can access Jonathan's teachings and have a site modeling webinar due next week so hopefully I will have more understanding after this.

 

Thanks for your help Mon