digital surface model with 5 m post spacing
digital surface model
with 5 m post spacing

What has to be observed while performing an ortho correction using RPCs from IRS-P6 Ortho-Kits?

As pointed out in the ResourceSat-1 Geometric Accuracy Assessment, IRS-P6 RPCs should be used with image-space polynomial correction terms. A first-order polynomial correction is sufficient for LISS-IV, LISS-III and AWiFS B and D scenes. For AWiFS A and C scenes, a second-order polynomial correction is required.

For Euromap's test results see the following slides.