---
name: "gshhs_dp"
section: "1gmt"
platform: "linux"
package: "gmt"
version: "4.5.7-2"
release: "Debian 7 (Wheezy)"
platforms: ["linux"]
url: "https://new.carta.tech/gshhs_dp"
---

# gshhs\_dp(1gmt)

Line reduction using the Douglas-Peucker algorithm

## NAME

gshhs\_dp - Line reduction using the Douglas-Peucker algorithm

## SYNOPSIS

**gshhs\_dp** *input.b tolerance output.b* \[**-v**\]

## DESCRIPTION

**gshhs\_dp** reads the binary coastline (GSHHS) or political boundary or river (WDBII) files and and reduces the complexity of the line by applying the Douglas-Peucker algorithm.  It automatically handles byte-swabbing between different architectures.

- *input.b*

  GSHHS or WDBII binary data file as distributed with the GSHHS data supplement.  Any of the 5 standard resolutions (full, high, intermediate, low, crude) can be used.

- *tolerance*

  tolerance is maximum mismatch in km.  The larger the value the more reduction will take place.

- *output.b*

  The reducted data set.

## OPTIONS

- **-v**

  Reports progress and statistics while running.

## EXAMPLES

To simplify the full GSHHS data set with a custom tolerance of 2 km, try

**gshhs\_dp** *gshhs\_f.b 2 gshhs\_2km.b*

## REFERENCES

Douglas, D. H., and T. K. Peucker, Algorithms for the reduction of the number of points required to represent a digitized line of its caricature, *Can. Cartogr., 10*, 112-122, 1973.

## AUTHOR

This implementation of the D-P algorithm has been kindly provided by Dr. Gary J. Robinson, Environmental Systems Science Centre, University of Reading, Reading, UK (gazza@mail.nerc-essc.ac.uk); his subroutine forms the basis for this program.

## SEE ALSO

[*GMT*(1)](/GMT/1.md), *gshhs*(1), *gshhstograss*(1)