I'm using Envi 4.2 and SPOT 4 Pancromatic (Level 1A) images in order to produce the DEM of the area. In the first step of Dem Extraction Wizard, it calculates the RPC values and estimates the scene elevation meters. In this process I've tried 3 different pairs (from the different parts of the country) but the min. elevation was calculated as -100,00m every time which is not possible for the areas. Is there a specific reason for this? How can i solve this problem? (I can change the min. value as 0 manually considering the sea in the images, but i don't know how it can affect the final DEM results.) On the other hand is there a way to calculate RPC values instead of calculating automatically with Envi? If so, how can i calculate it? Thanks in advance,