# HTF - Hydrographic Transfer Format

(GDAL/OGR >= 1.8.0)

This driver reads files containg sounding data following the Hydrographic Transfer Format (HTF), which is used by the Australian Hydrographic Office (AHO).

The driver has been developed based on HTF 2.02 specification.

The file must be georeferenced in UTM WGS84 to be considered valid by the driver.

The driver returns 2 spatial layers : a layer named "polygon" and a layer name "sounding". There is also a "hidden" layer, called "metadata", that can be fetched with GetLayerByName(), and which contains a single feature, made of the header lines of the file.

Polygons are used to distinguish between differing survey categories, such that any significant changes in position/depth accuracy and/or a change in the seafloor coverage will dictate a separate bounding polygon contains polygons.

The "polygon" layer contains the following fields :

- DESCRIPTION : Defines the polygons of each region of similar survey criteria or theme.
- IDENTIFIER : Unique polygon identifier for this transmittal.
- SEAFLOOR_COVERAGE : All significant seafloor features detected (full ensonification/sweep) or full coverage not achieved and uncharted features may exist.
- POSITION_ACCURACY : +/- NNN.n metres at 95% CI (2.45) with respect to the given datum.
- DEPTH_ACCURACY : +/- NN.n metres at 95% CI (2.00) at critical depths.

The "sounding" layer should contain - at minimum - the following 20 fields :

- REJECTED_SOUNDING : if 0 sounding is valid or if 1 the sounding has been rejected (flagged).
- LINE_NAME : Survey line name/number as a unique identifer within the survey.
- FIX_NUMBER : Sequential sounding fix number, unique within the survey.
- UTC_DATE : UTC date for the sounding CCYYMMDD.
- UTC_TIME : UTC time for the sounding HHMMSS.ss.
- LATITUDE : Latitude position of the sounding +/-NN.nnnnnn (degrees of arc, south is negative).
- LONGITUDE : Longitude position of the sounding +/-NNN.nnnnnn (degrees of arc, west is negative).
- EASTING : Grid coordinate position of the sounding in metres NNNNNNN.n.
- NORTHING : Grid coordinate position of the sounding in metres NNNNNNN.n.
- DEPTH : Reduced sounding value in metres with corrections applied as indicated in the relevant fields, soundings are positive and drying heights are negative +/-NNNN.nn metres.
- POSITIONING_SENSOR : Indicate position system number populated in the HTF header record.
- DEPTH_SENSOR : Indicate depth sounder system number populated in the HTF header record.
- TPE_POSITION : Total propagated error of the horizontal component for the sounding.
- TPE_DEPTH : Total propagated error of the vertical component for the sounding.
- NBA FLAG : No Bottom at Flag, if 0 not NBA depth or if 1 Depth is NBA, deeper water probably exists.
- TIDE : Value of the tidal correction applied +/- NN.nn metres.
- DEEP_WATER_CORRECTION : Value of the deep water sounding velocity applied +/- NN.nn metres.
- VERTICAL BIAS_CORRECTION : Value of the vertical bias applied +/- NN.nn metres. eg transducer depth correction
- SOUND_VELOCITY : Measured sound velocity used to process sounding in metres per second IIII.
- PLOTTED_SOUNDING : if 0 then the reduced depth did not appear on the original fairsheet or id 1 then the reduced depth appeared on the original fairsheet.

Some fields may be never set, depending on the value of the Field Population Key. Extra fields may also be added.

### See Also

- HTF - Hydrographic Transfer Format home page

- HTF Technical Specification