rasterized dtm's. mosaic them or create terrain dataset?

[ChristiNelson1]

Hi there,

I'm a bit stuck. I am new to terrain datasets and mosaics.   I have hundreds of raster based Digital Terrain Models (DTMs) for Contra Costa County.  We have planners and engineers who need the data for hydraulic modeling purposes.  We also need the data for other uses, like getting z-values for other layers including benchmark locations.

If I have a terrain dataset of all these tiles, will that be enough for the modelers?  In other words, will they be consistent across tiles?  Do terrain datasets take into consideration each tile's extent and statistics?  Further, is it even possible to create a terrain dataset from rasterized DTMs??

Or, is it better to mosaic them all together and then clip the mosaic to any smaller areas we may need in the future?  How to make them seamless?

Whichever is the better choice, what is the workflow?

Attached is a screenshot of my data.  I have ArcGIS 10.0 ArcInfo level with 3D Analyst extension.  Windows XP.

[DavidDossey]

Have you received an answer to your question?  I too am having the same issue.

[ChristiNelson1 · Accepted solution]

Hi there,

For the data we have and what we intend to use it for, it was most definitely recommended that we use Mosaic Datasets.

These are brand new to ArcGIS 10.  They are similar to Terrain Datasets in the sense that they save time and refer to only to the layers they need in the dataset.  However - terrain datasets have very limited capabilities at this point and are not recommended for analysis (mostly for storage and viewing).

Mosaic datasets have much more capability.  They are meant to be used for analysis among other things.  They take all the extent statistics into consideration.  It is super fast!

Read below for all the details.  I also asked her a few side questions, like how to export to a physical raster dataset, how to clip and export, and how to extract z values.

My rasters all had the same cell size and projection and were ready to be placed in the dataset. 


Here is a re-cap of what we did:

1. Create a new file geodatabase (or using an existing one) > right click the file geodatabase > new > mosaic dataset > specify a name for the mosaic dataset, and import the projection from one tile as the projection for the mosaic dataset

2. Right click on the empty mosaic dataset > Add Rasters  > within the Add Raster To Mosaic Dataset tool, specify the Raster Type as Raster Dataset, Input as Workspace, then browse to the location where you have the folders that contain source tiles > Check on Update Overview option to build overviews > OK

3. Once step 2 is done, right click on the mosaic dataset > Calculate statistics  > leave all the parameters as default to calculate statistics on the big 'mosaicked' raster

4. To use the Image Analysis window: Windows menu > Image Analysis

Here is the detailed explanation of the Image Analysis window:

What is the Image Analysis window? http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#//009t000001tm000000

5. To change the mosaic operators: right click on the mosaic dataset image layer in the TOC >  Properties > Mosaic tab or right click on the mosaic dataset in the Catalog window > Properties > Defaults tab > Default Mosaic Operator

Here are some detailed explanations about mosaic dataset:

What is a mosaic dataset? http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#//009t00000037000000

The workflow and tools to create mosaic datasets:

http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#/The_workflow_and_tools_to_create_mosai...

Adding rasters to mosaic dataset:

http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#/Add_Rasters_To_Mosaic_Dataset/00170000...

Mosaic operators: http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#/Mosaic_operators/009t000000n8000000/

Additionally, you can use the Extract Values to Points tool to extract the cell values of the raster (mosaic dataset) to your benchmark points. It is under ArcToolbox > Spatial Analyst Tools > Extraction > Extract Values to Points. Here is the detailed explanation of it:

http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#/Extract_Values_to_Points/009z0000002t0...

[DavidDossey]

Thank you!