Retrieve 3D shape of buildings

In order to get real world data, we use OpenStreetMap.

There are some tools that can extract 3D building data from OpenStreetMap. For example here, using https://cadmapper.com/pro/home

Make sure that the include 3D buildings option (bottom left) in the screenshot is selected.

Then, the model can be imported into Sketchup, and exported as dae.

We end up here with a .dae file.

Retrieve the road network definition

Here again, we use OpenStreetMap. The extraction can be done directly through the OpenStreetMap website.

There is an Export option on the top bar that allows you to select an area, then export it into a .osm file

We end up here with an .osm file.

Note : If possible, doing both extractions (building shape and road networks) at the same time with the same tool can be better and may avoid the placement step. (Not tested)

Create the Prescan Experiment

Files needed :

After previous steps, you should have the following

• A .dae file :
  The .dae file contains the 3D shapes of the buildings. It has to be imported in Prescan as a "User Library Element". (Explained after)

• At least one .osm file :
  You can use multiple .osm files if they come from the same area (e.g. if you want to add some missing roads afterwards).

Import the 3D building shapes as a UL Element

In a Prescan experiment, you can use "User Library Elements". They are created by importing a 3D model file (like the .dae one).
A UL Element is created only locally on the computer, so if the experiment is opened on another computer, it will have to be created again (with the same name and in the same folder. See after).

To create a UL Element, go to
Tools -> User Library Elements Wizard...
Then, add a new folder if you don't have any and click on New Element.

Then, you can leave everything as default, you just need to specify a name (on step 2) and the .dae file on step 3.

The new UL Element can be drag and dropped like every other elements in the Prescan Library.

Import the road network from OpenStreetMap

Importing .osm files is possible with Prescan (just with File -> Import -> OpenStreeMap... and select your file).

However, the roads which are produced will be full of errors. So, here, the painfull part begins...

Tips

• Prescan creates lot of flex roads but uses too much definition points, lots of them can be removed.
• Also, sometimes crosses ends are too short and it produce errors. It can be solved just by increasing it a little bit.
  (Right click on one end, next to the connection point, Edit road end..., then increase the Side road length value)
• When you edit the road network be careful to not move big parts of the map (pay attention if you change orientation of a road that you didn't disconnected before).
• Sometimes, you cannot edit a flex road directly, you have to disconnect one end first.

Lots of modifications has to be done patiently, good luck !

Finally

When your road network is consistent and doesn't have errors anymore, it is time to put the building shapes in place. You have to try to find the best place and orientation for the model (build the map and watch the top view on the 3D viewer).
Then, you can adjust the roads so it fits perfectly (sometimes, previous modifications may have made the roads not accurate with the real path).