There are generally two different ways that a map can have a strange rotation applied to it:
- Taking all the images in straight line and using the automated Camera GPS workflow.
- Insufficiently placing Anchor Points using one of the manual workflows.
Please refer to the workflow that was used below for information specific to that process.
Automated Camera GPS Workflow
In order to determine the proper rotation on the generated 3D model, we generally recommend making at least two passes over the survey area. Without a second pass or at least some images that are not all in a straight line Maps Made Easy will likely have a hard time determining which way is down and the resultant map will look quite strange.
On the Basemap and Manual GCP workflows Maps Made Easy will use an external data source (NASA SRTM data) to look up the elevation of the GCPs the users selects (unless one is provided in the manual workflow). The NASA STRM data was taken in 2000 so if the location on the earth has been modified by construction since that time the new value will not be reflected. Also, if the GCP is defined on a building or other vertical feature, its height above ground will also not be reflected. This difference in height will give a tilt to the model and throw off the elevation layer and DEM.
Think of setting Anchor Point locations like installing legs on a table. If they are too close to each other, the table could tip over. If the legs are all in a line, it is definitely going to fall over. If one is installed right at the edge of the table, it might break off and leave you with only two.