Drawing on top of 3d topography brought in via import imagery



Hi everyone, first time posting so please bear with.

I’m creating a model in SketchUp Pro that I’ll be exporting into some other software. The area I’m working on is about 28sqkm.

I’ve pieced together the area using the “import imagery” function multiple times, at varying levels of zoom to get more detail where I need it. Some of the images overlap, but SketchUp appears to have done a good job of lining everything up despite the “image far from origin” type warnings. I had to move one image with the move tool to make sure the terrain lined up (it was about 0.5m out and oddly was very close to the origin).

I’m trying to accurately trace over the features shown in the imagery (e.g. buildings, road, vegetation) as I want the model to be geospatially accurate. I’m planning on extruding the features that need it (e.g. buildings). I need to do this as the software I’ll be exporting to needs the different types of terrain to be separate surfaces (e.g. think assigning material to certain areas; grass is grass, concrete is concrete etc.) as the software ultimately assigns material properties to the individual surfaces (in a similar way to how SketchUp surfaces/materials work).

I’ve enabled “show hidden geometry” and have been manually tracing around the features in the image, making sure to follow the triangular geometry (such that the line I’m drawing is always an edge of a triangle, except when drawing on the face of the group). I started by doing the entire outside edge of the model. I’ve been keeping an eye on the draw tool to make sure I’ve been using the “draw on group” category (e.g. on edge in group, endpoint in group, midpoint of group, face of group). I moved on to drawing around the ‘big obvious lumps of topography’ like significant areas of vegetation and water.

This has worked for some surfaces, for example there is a section of sea that SketchUp has identified as being a different surface now it is fully enclosed (drawn around) and is showing the image texture with a grey-ish sheen over the surface that I can select. I can successfully apply a material to that surface.

However, some of the other areas are not showing as separate surfaces despite being enclosed as the sea area is.

I’m not sure what I’m doing wrong - though I’m wondering if the issue is that some of my geolocated imagery is overlapping and SketchUp is struggling to treat one area that is made of two images as just one area (or I’m somehow drawing on different ‘layers’ of topography, although everything in my model is “Layer0”) .

Having searched around a bit, I’ve seen some stuff about making the surface into a ‘physical model’ - i.e. adding a volume ‘under’ the image to make a 3d shape rather than just a 3d surface. I’ve also read about grouping, using the smooth edges feature, and using the stamp tool (which I don’t think is suitable for my purposes as I’m copying the image, not stamping onto it), but I didn’t want to start down any of those lines if there was something fundamentally wrong with my model - so thought it best to ask!

Any advice/help would be greatly appreciated, as you may have noticed I’m a SketchUp newbie.




Maybe Cadmapper could help you: https://cadmapper.com/
If you show us the issues in your model, will be easy solve this question.


Hi Rodolfo,

Thanks - that software looks really useful. I’m looking into it now to see if I can use it for a built-up segment of my model.

I’ve attached a screenshot that shows my issue quite well; you can see bottom left an area of sea that I mentioned before - it is clearly a separate section/surface. I’ve added a red arrow to point to an enclosed section that should also be a separate surface but evidently isn’t.




Can anyone help please?


Can u share the skp file?


My actual model is pretty big, so I made a quick test file to show my issue. I made an enclosed shape on the image surface, yet it isn’t its own ‘area’ like the sea is in the above picture. The test model is 3 or 4 geolocated imagery pieces. The shape I’ve drawn crosses over them (i.e. it’s not just on one ‘image’).

Here it is;

test.skp (2.2 MB)


The points picked around the “sea” section obviously all had the same elevation so a face was formed. The other sections probably don’t have same elevation at the picked points so will not define a face.

Since I don’t have SU18, I cant be 100% sure. When posting a model, it is always a good idea to save it as an older version so more people will be able to open it.


Hi Mitch,

Thanks for your response - see below save in SU15 format.

Is it not possible to create a face on a section with varying elevations?



test old ver.skp (2.2 MB)


The elevations can vary but all points must fall on the same plane which is why everything is triangulated. I think it will require sub-dividing the original mesh to match the defined areas but how you do that is still a mystery at the moment.


A face in SketchUp must be planar. The vertices of the area you have outlined are not on a single plane, so faces will not form. You can “stitch” them together by drawing lines across to form triangles (or more complicated polygons if several vertices happen to be coplanar). Once you have triangulated an area you can soften the edges between the triangles to tell SketchUp to treat the combination as a single “surface”.


Aha! Thanks both.

So if I trace over the hidden geometry triangles (TIN) then I should be definition get a series of surfaces that can then be smoothed? Does it then behave like one surface? e.g. I could apply a material to the smoothed surface all at once?

Do you know if it continues to behave as one surface if you export to some other software? e.g. export as collada then import elsewhere?


No. Simply tracing over the mesh outside the group does nothing but define the area of a material to be applied. You have to add that boundary to the surface inside the location group. Attached is the plugin I used to create this Surface patch.

Surface Patch.rb (4.3 KB)


Yes, a material can be applied to an entire surface at once. But most other apps don’t have an equivalent to SketchUp ‘s soft edges or surfaces and will see the surface as a collection of faces, all with the same material.


Again, thanks very much to the both of you.

Mitch - I’m not sure I understand what the plugin is doing there - are you saying that tracing the TIN boundary does not count as ‘drawing’ on the image surface somehow?


The plugin creates a face by using the x,y of each point of the outline and assigning the same z. The face is created in a group and then extruded into a solid which is intersected with the location group adding the edges created by the intersection to the location group creating a boundary.

No there is nothing gained by drawing lines outside the location group other than providing the outline of a sub surface boundary…


Maybe that’s the problem. You could, instead of redraw on the 3D surfaces, just redraw over the 2d image, which already exists in your model.
you will have a flat face. Move this over the template and use the sandbox drape command. And you will have the geometry closed on the 3d terrain.


Awesome - thanks so much for the help everyone. Turns out there is a great community here!

One … hopefully last… question; once I’ve successfully draped, is there a quick way to extrude the buildings from the 2d plan? Seems I cannot use the extrude tool because the surface is not flat… I’m thinking the best way might be to trace over the shapes from directly above, then either extrude that down through the model and delete the extra geometry, or, to simply move the traced shape then join up the surfaces manually…


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