ASPRS recommends that all checkpoint survey work to be used in verifying the vertical accuracy meets contractual specifications (as opposed to checkpoint data used by the lidar data provider for their own internal accuracy assessment tests) be undertaken by, or be under the supervision of, an independent survey firm licensed in the particular state where the project area is located. Independent in this case is taken to mean having no contractual or financial connections to the lidar data provider; in particular the survey firm should not have a subcontractor relationship to the data provider.