Frequently Asked Questions—Image Management Workflows for Elevation

Q : What type of imagery falls into this category?

A : ArcGIS 10.1 can work with a variety of formats for elevation data as listed in this Help topic. Sample data and workflow is available for download in this ArcGIS Online Group, includes the most common formats, e.g., 32 bit floating point elevation values in TIFF files and Lidar data in LAS format.

Q : Do I need to program in Python to use this workflow?

A : Python programming is not required. Sample tools can be downloaded from this ArcGIS Online Group which provide examples of implementing the recommended workflow in Python. These tools may also be used in ArcGIS ModelBuilder.

Q : If I have questions about this workflow, where can I get more information?

A : The workflows described in the Guidebook, and the samples available in ArcGIS Online provide detailed information. For any additional information and discussion, please refer to the ArcGIS Image Management Forum where users will contribute ideas, questions, and answers. For new posts related to the Image Management Workflows, please enter image_management and also workflow as 'tags' that will allow others to search for related posts.

Q: Why do you refer to the composite bare earth elevation model as a DTM (digital terrain model)? Shouldn't it be DEM (digital elevation model)?

Esri recommends readers refer to this text for an official definition of the terms DTM, DEM, and DSM:

Digital Elevation Model and Technologies and Applications: The DEM Users Manual, 2nd Edition, edited by David F. Maune, 2007. American Society for Photogrammetry and Remote Sensing (ASPRS), Bethesda, Maryland. ISBN#: 1-57083-082-7

In the USGS definitions of these two terms, one key differentiator is that a DEM is based on a regular grid, whereas a DTM can have irregular point spacing.

In the workflow recommended for managing multiple elevation datasets, the composite bare earth elevation model is referred as a "DTM", based on the following logic. The source datasets are combined within a "Derived Mosaic Dataset" that references multiple data sources in different projections. Although the worldwide elevation data is managed in the Web Mercator projection, all data sources are stored in their original coordinate systems. Since the source data does not use one single coordinate system, by strict definition the composite elevation model cannot be a DEM. However, note that in most cases, the individual source files are regularly gridded DEMs, and also that any data exported out of the World Elevation will be presented as a regularly gridded DEM in a single coordinate system (defined by the client at the time of request).