Global Mapper and Shapefiles¶

date:: 2012-08-05 11:25
author:: admin
category:: programming
tags:: globalmapper, scripting
slug:: global-mapper-and-shapefiles
status:: published

|http://geographika.co.uk/archive/images/globalmapper/blue\_marble\_europe\_small.jpg|I recently had a small project that required vector features in several thousand Global Mapper project files to be extracted into shapefiles.

The batch export tool didn’t seem to be running on the project files, so I was asked to take a look at the Global Mapper scripting documentation. The syntax was easy to follow, and scripts can be run by passing the script file name as an argument on the command line to the Global Mapper .exe file.

However when looking at the attributes of some of the exported shapefiles in ArcCatalog, the table was blank. Upon further investigation a couple of interesting issues came to light.

1. The shapefile string fields created by the Global Mapper export had a maximum length of 255 characters. I compared this to a newly created ESRI shapefile, and the DBFs string fields in this only had a maximum length of 254 characters. This difference also crashed the ESRI Merge tool (with no meaningful explanation). I had to cut the last character off in Python before they would merge.

2. Field names were not cleaned up by the GM export, meaning punctuation and spaces led to corrupt shapefiles/DBFs. I was able to get around this by editing the field names in the GM project files prior to an export, using the following syntax:

EDIT_VECTOR ATTR_TO_RENAME="FIELD. NAME.=FIELD_NAME"

The ESRI Shapefile Specification states that:

“The dBASE file (.dbf) contains any desired feature attributes or attribute keys to which other tables can be joined. Its format is a standard DBF file used by many table-based applications in Windows and DOS. “

However the “standard” DBF Specification simply mentions field names as being stored as ASCII text. It makes no mention of any invalid characters, and no mention of 254 character field limitations. Opening the DBFs in Excel didn’t cause any issues.

I sent an email to Global Mapper support mentioning these issues, and literally within hours I received the following reply:

“I updated the maximum field length for DBF export to 254 since ESRI can’t handle the full 255 characters that the DBF format itself supports. I also limited the field names to just characters, numbers, and underscore since it appears that ESRI also can’t handle just anything in the DBF field names despite the DBF format itself having no such limits. “

“I have placed a new build at http://www.globalmapper.com/global_mapper13.zip with the latest changes for you to try. Simply download that file and extract the contents into your existing v13.xx installation folder to give it a try. If you are using the 64-bit v13 version there is a new build at http://www.globalmapper.com/global_mapper13_64bit.zip .”

I was stunned to get not only a reply from email technical support that not only understood the issue I reported, but had updated, fixed, and recompiled the executable, and made it available for download (all by the principle developer Mike Childs). Although I’ve not used Global Mapper enough (beyond scripting) to judge it as a GIS application, I can certainly vouch for the “unsurpassed technical support with no extra support fees” mentioned on their site.

In addition there are plans to allow to export to the slightly superior (in that memo fields can be handled without resorting to additional files) ESRI File Geodatabase format:

“While there is currently only support for reading and not writing ESRI File Geodatabases, we are planning on adding ESRI File Geodatabase export support, perhaps as soon as the upcoming v14 release later this year. “

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Comments¶

1. Jim **

Thanks for the tip! I’ve been using GeoJSON with OpenLayers, and have just been generating the GeoJSON using Excel, I’ve been meaning to write a PHP script to do the conversion, but it looks like this will work even better!

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3. geographika **

@Jim

Please note that the code has been updated to call the find.geojs

page rather than find.js which returns JSON rather than GeoJSON.

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