Using sketchup to model a non-planar ground surface abutting buildings and an inclined, bent french drain through it

I am fairly new to sketchup, so maybe what I am attempting is beyond my skills, if so please say as I think I could use Sketchup in 2D mode to do the same thing in several 2D drawing and sections. But a single integrated 3D model would be so much better and help me think things through. I am using SU Make 2017.

My overall project is to create a model of my cottage from architect drawings for use in repairs and improvements. As part of this I am trying to use sketchup to model a non-planar polygonal ground surface abutting buildings and an inclined, bent trenches including some french drains with pipes in them around the buildings and to a septic tank and soakaways.

As part of this I have already managed to create TIN-based terrain models from LIDAR air survey data (DSMs and DTMs). Here is a post on that attempt: Importing UK LIDAR DTM data with decimal elevations as a terrain model. Unfortunately while supplying quite a lot of useful and seemingly accurate heights it seems to me to contain too many artefacts (DSM-based), or reflect too much smoothing for direct use (when DTM based), though I could be wrong.

I also have an architects survey which gives land levels relative to ground floor level where they abut the house. So probably enough information to create a reasonably accurate surface close to the house given my knowledge of the actual topography.

I have also traced and created the ground floor walls from an arctitects plan, and a 3D model of our new shower room and utility room and lobby. As an initial expoloration of land surfaces, I have created planar, rectangular, inclned surfaces round the house to roughly model the ground levels, but predictably they don’t model the places the terrain is non-planar well enough, and don’t join together as they have to be tilted differently and are rectangles. Not only aer certain slopes needed for correct functioning, but UK building regs require that pipes are normally laid at least xcm below ground and with a slope between certain limits.

Having read some help files and some posts I can see two possible ways of approaching the problem, though I do not know how to do it in detail. I may also be missing an obvious third or forth approach!

Both start with setting up construction points at places where I know the height above site datum.

  1. Drape a TIN over the construction points and around the house, and indent the ditches into it. To model the ditch sides sensibly you would seem to need a reasonably fine mesh, maybe 5cm - would this not make the model very big? The drainage work will probably cover 0.2 acres or so. But then how do you get it to deform only to the degree necessary to model a slightly to moderately non-planar surface? And how do you create an inclined ditch with bends in it?

  2. Create a single, non planar, irregular polygonal vector surface around the houses, and over the construction points, and push it down or break it to model the ditches. I am not sure this is even possible in sketchup, though I know there are tools for bending and twisting etc surfaces. I am not sure what tool you would use to create a bent inclined ditch in it…

If someone would not mind answering some initial queries I would be very grateful. Is what I am attempting feasible given a reasonable degree of persistance? If it is broadly what approach would you suggest to execute it, and what additional tools should I use?

Many thanks for any help you can give in anticipation.

Kind regards


Yes it would. And likely all of what you propose will make your model unwieldy and perhaps unusable.

Learn how to use the Sandbox tools and look at tools like Artisan and Vertex tools.

It’s possible if you want to invest enough time and effort.

Exactly what is to be gained by modeling the surface of your property to such fine resolution? Will you model the mole hills and tree roots near the surface, too? You can do it but that doesn’t mean you should.

Does your time have any value?

did you ever look at the geolocation terrain available in SU Pro?

it may enough…

post the coordinates if your trial has expired and one of us could show you what the level of detail it gives…


Thanks very much for your responses, which were very helpful

You maybe misunderstand me a little. Sorry if I was not clear. I have no wish at all to use a smaller grid than I need. I was just thinking of what would be needed to model quite small ditches using the TIN approach, and make the ditches look convincing - fairly sharp ditches rather than jagged ones. But I am maybe underestimating TINs - the LIDAR was my first use. The minumum width of the ditches is 45cm, max maybe twice that. The depth maybe 0.75m ish.

My aim in modelling the drainage is partly to make sure it will work given a number of constraints. It’s an old building with a haha and a septic tank below the haha. So will the levels allow the correct slopes and allow pipes to be buried deep enough but not too deep? Also so I can submit plans for approval to building regs. They require slopes, height differenes, soak-away volumes, rodding points etc to be right. After that of course to guide the contractors. I will be tracing existing plans but moving the drains away from the walls and re-routing one after advice about wall stability, and another due to a mod in improvement plans. Also when all is complete the model I hope will be like a partial BIM for our house and help to preseve a beautiful old building for many more years.

I am aware of the Sandbox tools, will look again to check in more detail. I’ll have a look at the other tools now - thanks very much for the pointers.

Kind regards


I am sorry my trial expired long ago. I have been using SU on and off for 6 months or so. May I pm or email you the cordinates and my email? Occasionally people misuse location info posted online.

FYI the LIDAR gives a 2m grid in my area. But there are a fair number of artefacts. Away from buildings and trees most DSM values look accurate. So I can use the good values for the main ditch to the tank and for its soakaways.

Kind regards


yes you can PM me and I’ll what I can grab…


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