Georeferenced images help planners to compare and document the progress of underground construction sites. As underground positioning
can not rely on GPS/GNSS, we introduce a solely vision based localization method, that makes use of a textureless 3D CAD
model of the construction site. In our analysis-by-synthesis approach, depth and normal fisheye images are rendered from presampled
positions and gradient orientations are extracted to build a high dimensional synthetic feature space. Acquired camera images are
then matched to those features by using a robust distance metric and fast nearest neighbor search. In this manner, initial poses can be
obtained on a laptop in real-time using concurrent processing and the graphics processing unit
