Unit conversion (Maritime Charting)

Many nautical charts have elevation units in feet and depths in units other than meters, such as fathoms and fractions, fathoms and feet, and feet. When this occurs, use the units shown on the chart to collect your elevation and depth attributes. What you see on the chart is what you enter as your value when attributing a feature. This makes quality control more efficient and accurate.

Converting units

Once a chart is ready to be edgematched or converted to VPF, all the units should be converted to meters. This allows accurate edgematching.

Once you convert your units, you are not allowed to convert those features again. With the Units Conversion tool, you can convert based on your Dqyarea extent or a selected set of features.

Original unit values are moved to a field called orig_<item> in the feature table. You can label this field in ArcMap for visual quality control purposes. All the orig_<item> fields default to -99999. If you import your data with the VPF Importer, they default to 0. Once converted, the Units Conversion tool will not run on features with orig_<item> not equal to -99999 or 0.

TipTip:

If your elevations are in feet, all features with field HDH are converted using Standard Conversion Table 4. All other elevation fields use Standard Conversion Table 1.

Feature class

Elevation fields

Depth fields

AqueductL

OHC

BridgeA

MVC,OHC,SHC

BridgeL

MVC,OHC,SHC

BuoybcnP

EOL

CanalA

WID

HDP

CanalL

WID

DangerA

HDP

DangerP

HDP

HazardA

HDP

HazardP

HDH

HDP

Hydarea

CVH,CVL

Hydline

CRV

IndustP

HGT,ZV2

IndustA

ZV2

LightsP

EOL

MaritimA

WID

HDP

MaritimL

WID

HDP

MisciwyA

WID

PipelinL

DEP,HSB,OHC

PowerL

OHC

ReefA

HDH

HDP

Relline

ZV2

Relpoint

ZV2

RouteA

HDP

RouteL

HDP

RuinsA

HDH, HGT

HDP

RuinsP

HDH

HDP

SnowiceP

HGT

SoundP

HDH

HDP

SepartnA

WID

SepartnL

WID

SweptA

HDP

SweptL

HDP

TunnelL

HDP

The following table describes the fields that are converted for each feature class listed.

Related Topics

2/17/2015