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Vertical Datum Transformation
Integrating America's Elevation Data

VDatum User Guide

This User Guide describes VDatum version 4.x with the graphical user interface.

Once you download VDatum software and its transformation grids, your computer is ready to transform geospatial data among several horizontal and vertical datums.

Step-by-step

Launch VDatum

To run from Window Explorer, locate the VDatum.bat file and double click on that file.

When launched, an MS-DOS command window and the VDatum application window are opened. The MS-DOS command window is where information such as Disclaimer and error messages are displayed. All activity is done with the VDatum application window.

To run VDatum tool from the command prompt or terminals, type the following: 

java –jar [<path to vdatum.jar file>] vdatum.jar

vdatum Disclaimer and Messages Window

Figure 1: the MS-DOS command window where Disclaimer and error messages are displayed.

Operation step by step

Figure 2: the VDatum app GUI

Define georeferencing information

define vdatum datum information

Figure 3: Datum Information

Point Conversion

vdatum_ipoint

Figure 4: Input data as an elevation point in geographic coordinate

Input data in geographic coordinate system (Latitude/Longitude) are accepted in formats listed below: 

When select File Report, a report will be created and saved at user's specified location. Output coordinates can be converted between decimal degrees and DMS (degree minute second) format on-screen by clicking the DMS button, or in file report by selecting "to DMS". A sample report can be viewed at sample_pointreport.txt.

ASCII File Conversion

vdatum convert an ASCII file or a set of ASCII files

Figure 5: Convert a text file - this sample file is available for download here

A window shows converting progress in percentages. Users can cancel the processing anytime by pressing the Cancel button.

LiDAR (.LAS/.LAZ) Conversion

vdatum convert LiDAR (*.las) files

Figure 6: Convert a LiDAR (*.LAS) file - a sample LAS file is available here.

A window shows converting progress in percentages. Users can cancel the processing anytime by pressing the Cancel button.

For .LAZ formtat file, it can only be processed in VDatum app on Windows OS

SHAPEFILE (.SHP) Conversion

vdatum convert SHAPEFILE (*.shp) files

Figure 8: Convert a SHAPEFILE (*.shp) file - a sample SHAPEFILE file is available here.

A window shows converting progress in percentages. Users can cancel the processing anytime by pressing the Cancel button.

SE Alaska

When transforming in the Southeast Alaska regional model and traversing to Local Mean Sea Level (LMSL) or other Tidal Datums, it is important to understand the transformation roadmap differs from that of other currently supported VDatum regional models. You will notice that the Target Horizontal reference frame automatically changes to IGS08 when selecting LMSL or a Tidal Datum as the source or target vertical datum while in Alaska. The reason for this is that our roadmap traverses through IGS08, then utilizes xGEOID17B, and then into LMSL with the Topography of the Sea Surface (TSS) and then to tidal datums. All other VDatum regional models traverse through NAD83 and then to NAVD88 utilizing a NGS Hybrid GEOID.

Sample Scenario:

SEAK Tidal Vertical Datum Transformation “Roadmap” shows the difference from CONUS & PR/USVI Tidal roadmap.

Chesapeake/Delaware Bays and Mid-Atlantic Bight

When transforming in the Chesapeake/Delaware regional model and traversing to Local Mean Sea Level (LMSL) or other Tidal Datums, it is important to understand the transformation roadmap differs from that of other currently supported VDatum regional models. You will notice that the Target Horizontal reference frame automatically changes to IGS14 when selecting LMSL or a Tidal Datum as the source or target vertical datum while in Chesapeake/Delaware Bay vicinity. The reason for this is that our roadmap traverses through IGS14, then utilizes xGEOID20B, and then into LMSL with the Topography of the Sea Surface (TSS) and then to tidal datums. All other VDatum regional models traverse through NAD83 and then to NAVD88 utilizing a NGS Hybrid GEOID, except Southeast Alaska which uses IGS08, then utilizes xGEOID17b. The use of xGEOID's is to assist in preparation for transitioning to the modernized National Spatial Reference System (NSRS) in the future.

Sample Scenario:

Chesapeake/Delaware Bay Tidal Vertical Datum Transformation “Roadmap” shows the difference from CONUS & PR/USVI Tidal roadmap.

West Coast

When transforming in the West Coast regional model and traversing to Local Mean Sea Level (LMSL) or other Tidal Datums, it is important to understand the transformation roadmap differs from that of other currently supported VDatum regional models. You will notice that the Target Horizontal reference frame automatically changes to IGS14 when selecting LMSL or a Tidal Datum as the source or target vertical datum while in West Coast vicinity. The reason for this is that our roadmap traverses through IGS14, then utilizes xGEOID20B, and then into LMSL with the Topography of the Sea Surface (TSS) and then to tidal datums. All other VDatum regional models traverse through NAD83 and then to NAVD88 utilizing a NGS Hybrid GEOID, except Southeast Alaska which uses IGS08, then utilizes xGEOID17b. The use of xGEOID's is to assist in preparation for transitioning to the modernized National Spatial Reference System (NSRS) in the future.

Sample Scenario:

West Coast Tidal Vertical Datum Transformation “Roadmap” shows the difference from CONUS & PR/USVI Tidal roadmap.

Columbia River Datum

The Columbia River Datum (CRD) is being implemented based on the grid provided by the U.S. Army Corps of Engineers (USACE). This transformation is based on utilizing GEOID09 to transform to NAVD88 and then to CRD. GEOID09 was the hybrid National Geodetic Survey (NGS) GEOID utilized for the CRD grid development.

The Columbia River Datum (CRD) is the adopted fixed low water reference plane for this area. CRD is a U.S. Army Corps of Engineers non-tidal datum defined at distinct river miles relative to NAVD88, and is used as chart datum above river mile 23 on the Columbia River. Datums are computed using observations from the low river stages of the year, generally August through October due to the masking of the tidal signal from strong seasonal river runoff during other portions of the year. Depending on river flow, water levels can be significantly higher than Columbia River Datum.

Initial testing of the implementation of CRD in VDatum provides us with some insight to the uncertainty of these transforms. The VDatum implementation was tested against Center for Operational Oceanographic Products and Services (CO-OPS) published data at the following stations:

Tidal Datums relative to CRD provided differences ranging from 2.5 centimeters at St. Helens to 7.2 centimeters at both Longview and Vancouver. Transforming between tidal datums resulted in differences ranging from a few millimeters to 1.1 centimeter at Longview. Larger uncertainties can be expected between Local Mean Sea Level and NAVD88, due to the transformation roadmap implemented for the West Coast tidal datums, utilizing xGEOID20b and how a user may want to define the transform of NAVD88 based on a particular NGS hybrid GEOID. Uncertainties for transforms between Local Mean Sea Level and NAVD88 of 2-13 centimeters can be expected.

CRD is accessed through the West Coast Regional Model as illustrated below.

Puerto Rico and US Virgin Island

When transforming in the Puerto Rico/U.S. Virgin Islands regional model and traversing to Local Mean Sea Level (LMSL) or other Tidal Datums, it is important to understand the transformation roadmap differs from that of other currently supported VDatum regional models. You will notice that the Target Horizontal reference frame automatically changes to IGS14 when selecting LMSL or a Tidal Datum as the source or target vertical datum while in Puerto Rico/U.S. Virgin Islands vicinity. The reason for this is that our roadmap traverses through IGS14, then utilizes xGEOID20B, and then into LMSL with the Topography of the Sea Surface (TSS) and then to tidal datums. This is similar to the current implementations of Chesapeake/Deleware Bay and West Coast regional models. All other VDatum regional models traverse through NAD83 and then to NAVD88 utilizing a NGS Hybrid GEOID, except Southeast Alaska which uses IGS08, then utilizes xGEOID17b. The use of xGEOID's is to assist in preparation for transitioning to the modernized National Spatial Reference System (NSRS) in the future.

Sample Scenario:

PRVI Tidal Vertical Datum Transformation “Roadmap” shows the difference from CONUS Tidal roadmap.