---
name: "pnmmercator"
section: "1"
platform: "linux"
package: "netpbm"
version: "10.86.51-2"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/pnmmercator"
---

# pnmmercator(1)

transform a worldmap from rectangular projection to Mercator projection and vice-versa

## NAME

pnmmercator - transform a worldmap from rectangular projection to Mercator projection and vice-versa

## SYNOPSIS

**pnmmercator** \[**-inverse**\] \[**-nomix**\] \[**-\[v\]verbose**\] \[*filename\]*

*Minimum unique abbreviation of option is acceptable.*  *You may use double hyphens instead of single hyphen to denote options.*

## DESCRIPTION

*This program is part of* **Netpbm**(1) *.*

*The* **pnmmercator** *utility, converts a rectangular projection worldmap* *to a Mercator projection format, as used for maps.google.com and many other* *online maps.  The map used as input for* **pnmmercator** *must have rows for* *-90 to 90 degrees latitude and columns for -180 to +180 degrees longitude. The* *file will typically be twice as wide as high, but this is not a* *requirement. The output file will be using the*  *Mercator projection* ⟨http://en.wikipedia.org/wiki/Mercator\_projection⟩  *and will get double the height of the input file.*

*Maps using the Mercator projection are stretched more the closer a row is* *to the North or South Pole. The last few degrees (\> 85 or \< -85 degrees)* *are not part of a Mercator map at all because they would be stretched too much* *and the rows close to the edge will show banding, because they originate from* *the same row in the original map.*

*To overcome this, the program will by default do interpolation of pixel* *colors, which will eliminate the banding effect, but will cause some blurring* *of the output. With the -nomix option, this interpolation of colors isn't* *applied. You can obtain the highest quality output by starting with an input* *map of high resolution, so that you can follow the* **pnmmercator** *transformation with a* **pamscale** *reduction in size.*

*This program can also convert a Mercator projection map back to a* *rectangular projection based.  As said, the Mercator map doesn't have* *information about the latitudes close to the poles.  Therefore the top rows in* *the output image will be identical and copied from the row corresponding with* *latitude of 85 degrees. The same at the bottom of the map.*

*Pnmmercator doesn't have any provision for scaling the image. You can scale* *by piping the output of the program through Netpbm programs such as* **pamscale***.*

*You can find maps to be used as input at* **flatplanet.sourceforge.net**(1) *or*  *uic.edu/pape* ⟨http://www.evl.uic.edu/pape/data/Earth/⟩ *.*

*The point of a Mercator projection map is that compass directions work on* *it.  If you draw a straight line northeast from some point on the Mercator* *map, the line traces the course you would sail if you sailed a compass bearing* *of northeast from that spot.  Naturally, primitive navigators appreciated* *that.  The biggest drawback of Mercator is that areas to the north and south* *appear much larger than they are in real life.  For example, Greenland appears* *to be larger than South America even though it only a ninth as large.  Note* *that areas away from the equator are stretched north-south as well as* *east-west.*

*A rectangular projection is one where vertical distance is proportional to* *angular latitude distance of the represented area and horizontal distance is* *proportional to angular longitude.*

## PARAMETERS

*filename is the name of the input file.  If you don't specify* *this,* **pnmmercator** *reads the image from standard Input.*

## OPTIONS

*In addition to the options common to all programs based on libnetpbm* *(most notably* **-quiet***, see* \
  *Common Options* ⟨index.html#commonoptions⟩ *),* **pnmmercator** *recognizes the following* *command line options:*

- **-inverse**

  *With this option a conversion from Mercator to degrees is applied.The* *output image will have half the height of the input map.*

- **-nomix**

  *Default behaviour is that color blending is applied in between two adjacent* *rows. If you specify the -nomix parameter there is no blending. The* *consequence is a banding at the top and bottom of the map.  With this option,* *the output map will also consist of exactly the same colors as the input.*

- **-verbose** *and* **-vverbose**

  *This parameter outputs some additional information. If you double the 'v',* *it will output debug data about the lat/long degree and Mercator* *conversions.*

## SEE ALSO

**pnm**(1)  *and* [**pamscale**(1)](/pamscale/1.md) [**ppmglobe**(1)](/ppmglobe/1.md)

## HISTORY

**pnmmercator** *was new in Netpbm 10.49 (December 2009).*

## AUTHORS

*Willem van Schaik (of* **pnmtopng***/***pngtopnm** *fame) wrote this program in October 2009 and* *suggested it for inclusion in Netpbm.*

## DOCUMENT SOURCE

*This manual page was generated by the Netpbm tool 'makeman' from HTML* *source.  The master documentation is at*

-

  **http://netpbm.sourceforge.net/doc/pnmmercator.html**