Software maker Intergraph ( INGR) agreed Thursday to be acquired by an investor group of private equity firms for $1.3 billion.

The group, led by Hellman & Friedman and Texas Pacific Group, will pay $44 a share for Intergraph, an 18% premium over Thursday's closing stock price of $37.

"We are pleased to announce this transaction which represents the culmination of a thorough review of our standalone plan and strategic alternatives," said Sidney McDonald, Intergraph's chairman, in a statement. "Our board of directors believes this transaction is in the best interests of our stockholders and underscores the significant operational and financial improvements Intergraph has made over the past three years."

Intergraph makes spatial information management software used for mapping, security and building plants.

"Given our significant experience in the software and services, energy and communications markets globally, the TPG team is confident that it can support Intergraph as it expands its product suite and global customer base," said Texas Pacific partner Brian Taylor.

The deal is expected to close in the fourth quarter.