LiDAR Packet File Organization
Written by Tim Loesch, DNR GIS Manager
           tim.loesch@state.mn.us
           651-259-5475

This documentation relates to LiDAR and derived products that have been mosaiced and processed into a county data package.

MOSAICED DATASET
elevation_data.gdb - File Geodatabase (Version 9.3) containing mosaiced 1 and 3-Meter DEMs, hillshade, Breaklines, building footprints, Tile Index and Validation Points.
CONTOURS – mosiaced 2’ contours. See below for a description of the process used to create the 2’ contours.
       DEM01 - one meter DEM as delivered by vendor
 DEM03 - three meter DEM. See below for a description of the process used               to create the 3 meter DEM
       DEM03HS - Hillshade of DEM03
       HYDRO_BREAKLINES – merged edge of water breaklines for entire area
	 BUILDINGS – Merged buildings for entire area
 TILE_INDEX - a tile index with a field called DNR_QQQ_ID which identifies          all of the tiles.
VALIDATION_POINTS - a feature class of the points used in the vertical accuracy assessment
qaqc - a table summarizing all of the tiles and various attributes about them - used for QA/QC purposes. Fields include:
	tile_name – the name of the tile
	min_elev – minimum elevation in one meter DEM (meters)
	max_elev – maximum elevation in one meter DEM (meters)
	Range_elev – range of elevation in tile
	Mean_elev – average elevation in tile
	Min_x – minimum X bounding coordinate
	Max_x – maximum X bounding coordinate
	Min_y - minimum Y bounding coordinate
	Max_y – maximum Y bounding coordinate
	Cellsize_x – x cellsize
	Cellsize_z – y cellsize
	Rows – number of rows in one meter DEM
	Columns number of columns in one meter DEM
Bare_Earth – Present or absent – indicates presence of Bare earth points (should all be Present)
Breaklines – Present or Absent – indicates presence of hydro_breakline feature class (should all be present)
Las_file – Present or Absent – indicates presence of LAS file (should all be Present)

	All of the DEMs are floating point rasters with Z-Values in meters. 
	Horizontal projection is UTM Zone 15
	Horizontal Datum is NAD83
	Vertical Datum is NAVD88
	
	The 3 meter DEM was created using the following methodology:
•	Step 1: Mosaic all of the tiles that make up the county into a file geodatabase.
•	Step 2: The one meter raster is reduced to 3 meter resolution using the Spatial Analyst, Aggregate Tool. A 3x3 window of one meter cells are combined into one 3x3 meter cell and assigned a value based on the mean of the 9 cells.   

<county_name>_validation_report.xlsx - spreadsheet of vertical accuracy assessment. This workbook contains worksheets that show the vertical accuracy assessment using points provided by county and state surveyors.

The contour and point files are very large. One of the things that you'll notice about the point file is that they are comprised of multi-point features. What this means is that there are likely 3000 - 5000 points included in each of the records in the table. If you use the interactive select tool to select one point you actually select one record and all of the points associated with this record. You can do an Identify on the points but you won't get a Z value listed because it does not exist as an attribute in the table, it's a property of the point. It also means you cannot list labels on the points.

Two foot contours found in the geodatabases were created from the 3 meter DEMs as indicated above. In this process the 3 meter DEM is smoothed using a 3x3 window and then contours are generated from this raster. 

DATA USE TIPS

Converting to County Coordinates
To be able to project to County Coordinates you'll need to make sure that you create a Custom Geographic Transformation for your county. This is done using Create Custom Transformation Tool found in the Data Management | Projections and Transformations Toolbox.  When you do this you need to select the input coordinate system (UTM Zone 15, NAD83) and the desired output projection. The Transformation method needs to be Longitude_Rotation based on recommendations from ESRI user support. Once you have the custom geographic transformation you can go ahead and use that to project your data.

Remember that when you use ArcMAP it will automatically project data to the Coordinate system of the Data Frame. A common example is a data frame that contains data in HARN county coordinates. When a DEM or other data that is using UTM Zone 15, NAD83 Datum. ArcMAP will readily project the DEM or vector data to match County Coordinates but you have to be careful to select the correct Geographic Transformation to make it work properly. Hence the message:

This message is telling you that any data projected into the data frame may have alignment and accuracy problems because you have not set a geographic coordinate transformation. You must explicitly set the proper Transformation in the Data Frame Properties | Coordinate System tab. Look for the Transformation button on this window. For most counties there will not be a selectable Transformation suggestion and you have to create one. 

Converting Grid Z values from meters to feet
To convert the Z units from meters to feet use the Spatial Analyst | Math | Times tool. Multiply the values by 3.280839895