A method for determining a sequence of a target nucleic acid is described. The method uses a plurality of control oligonucleotides with known sequence and unique identifications to map hybridization signals associated with a plurality of sequencing probes to a loosely packed multi-dimensional dye space, such that a region in the dye space can be associated with one or more sequencing probes. When a detected target hybridization signal of a sequencing probe and a target nucleic acid is mapped to the multi-dimensional dye space, the sequencing probe and thus the corresponding nucleotides in the target nucleic acid can be determined based on the one or more sequencing probes associated with the region that the detected target hybridization signal is mapped to.