Q: Why are there dotted lines after setting transparently display of NoValue data (the color of dotted lines is consistent with that of the NoValue data)?

A: The problem is that the actual NoValue data in the DEM dataset is inconsistent with that in the attributes. The solution is as follows: Delete the image pyramids, set the attributes of the NoValue data for the dataset to the actual value of the NoValue data of the DEM dataset, and recreate the pyramid.