I have a curiosos situation here. A project with 512 pictures, grid flight. More than 20 GCP have done with GNSS, and area geoid ondulation of -6.29 meters.
After done all processing steps, I checked in Pix4D the DTM values, and got excelent position (X,Y) and altimetric (Z) value. Projection system was UTM Sirgas 2000 24S (EPSG 31984).
But, I needed to calculated slope, using ArcGis, and for my surprise, DTM valeus in this, were not same of Pix4D. I got DTM, inside Pix4D project, and copy to ArcGis project.
SO, why this difference between Pix4D DTM screen value and ArcGis? I have opend same DTM in Global Mapper, and got same difference. Is any problem in output vertical coordinate system definition? How can fixed it?