Projection display device, method for controlling projection display device, and program for controlling projection display device

A projection display device to be built in a vehicle having a movable working machine, a main body part, and a structure, the working machine being attached to the main body part, the main body part having a driver's cabin, the structure being fixed ahead of the driver's cabin, the projection display device comprising:

• a projection display unit that includes a light modulation unit that, on the basis of image information to be input, spatially modulates light emitted from a light source, and that projects image light, obtained through spatial modulation by the light modulation unit, onto a projection surface built in the driver's cabin to display a virtual image based on the image light;
• an overlapping area detecting unit that detects a first overlapping area of the projection surface and the working machine observed from a driver's seat in the driver's cabin;
• and
• a display control unit that controls the image information to be input to the light modulation unit and that controls the virtual image that is to be displayed by the projection display unit,
• wherein, in a state where a distance between a second overlapping area and the first overlapping area exceeds a threshold, the second overlapping area being an overlapping area of the projection surface and the structure observed from the driver's seat, the display control unit performs tracking control in which the projection display unit is caused to display a virtual image based on operation support information while retaining a predetermined positional relationship with the first overlapping area, and in a case where the distance is changed from a state of exceeding the threshold to a state of being less than or equal to the threshold, the display control unit selects and performs either first control or the tracking control on the basis of a content of the operation support information, and
• wherein the first control is control in which the retaining of the positional relationship is cancelled and the virtual image based on the operation support information is displayed at a position that avoids the second overlapping area or control in which the retaining of the positional relationship is continued and a display size of the virtual image based on the operation support information is made greater than a display size of the virtual image based on the operation support information in a state where the distance exceeds the threshold.