You can use this tool to inspect the surfaces of a model. It is a jsfiddle application located here, http://jsfiddle.net/guillermo_matterport/pftnhkuc
Setting up a model in the intersection inspector
- Go to this jsfiddle editor link Editor You can also select 
Edit in JSFiddleat the bottom of this page. - Select 
Forkto create your own copy of the application. 
  
- Set your model sid. Look for the modelSid variable.
 
  
- Run your updated application. You should see your model loaded in the Results pane.
 
  
Using the intersection inspector
- Load the application after you have setup your model.
 - Navigate to the location on the model that you would like to inspect.
 - Place the mouse over the area of interest and stop moving it. You should see a button pop up right over the mouse. If you move the mouse outside the area of the button, it will disappear.
 
  
- Click the button and look at the upper left of the showcase window. You will see the 3D position and normal for the point you clicked.
 
  
- Copy the position and normal text. You can use the position value to set the mattertag anchor position and normal value to set the stem.