I am in process of making the UI of application, that has a 2.5D map (3/4 perspective) made as image, which displays equipment in rooms and areas of power plant. There are no multiple views of the room, only one per room. These are strict constrains. User can select an object on it and get information about equipment. Some equipment can be rather complex in shape (transformers or tubes with valves). Application is keyboard & mouse based. Users rarely use the application, so different cases from 3D modelling software (i.e. clicking multiple times to select necessary object and double click to open dialog with information) are not affordable.
So, if all objects were visible, there is no problem — user hovers over it by mouse (the objects changes it’s visual style — for instance, the glow appears around it), sees the hint with it’s name, decides weither he should get additional information and clicks inside the object to get it.
But due to complex structure of equipment, the case of overlapping objects is rather expected — so it is not easy to recognize — is there one object or more at the cursor position, and, especially, to select the necessary. Even if the edge of the object is visible a bit, it is not easy to recognize it and click on it due to Fit’s law.
So the question is how to make clear that there are many objects at one position and make selection of necessary object as convenient as possible?
Here is the primitive sample picture of the situation:
Update: Right now I suppose to make the selection of objects without any others behind them as described in the case (hover with the name of equipment and glow around, simple click opens the dialog with info) and for overlapping objects to display in the hint the amount of objects, left-clicking on it shows the context menu with the list of objects to choose from.