GM scale bar is not correct ??
chuck
Global Mapper UserTrusted User
scale test copmparison.pdfscale test.pdfFolks:
I am working on a simple project -- a dxf file. I have loaded the file and then noticed the scale bar provided with the drawing was not matching the map scale shown in the GM workspace. I have used the measurement tool and verified the drawing's scale bar is indeed 1,000 ft.; yet, when viewing the GM map scale it appears to be too long. I have attached pdf's of both a GM output pdf print and a screen capture to illustrate the issue I am facing.
GM v12.01
Build Time Jan 20 2011 22:46:02
Please advise.
Thank you in advance.
-Chuck
I am working on a simple project -- a dxf file. I have loaded the file and then noticed the scale bar provided with the drawing was not matching the map scale shown in the GM workspace. I have used the measurement tool and verified the drawing's scale bar is indeed 1,000 ft.; yet, when viewing the GM map scale it appears to be too long. I have attached pdf's of both a GM output pdf print and a screen capture to illustrate the issue I am facing.
GM v12.01
Build Time Jan 20 2011 22:46:02
Please advise.
Thank you in advance.
-Chuck
Comments
-
Chuck,
This is because of the projection that you are viewing the data in. The Geographic (lat/lon) projection is extremely distorted compared to ground truth in the X direction if you are far from the equator, so any measurements along the X direction will not match the distance scale. Measurements in the Y direction will though. To get a more consistent scale in both directions you would need to use a better projection for smaller areas of the earth, like UTM, on the Projection tab of the Configuration dialog.
Let me know if I can be of further assistance.
Thanks,
Mike
Global Mapper Support
support@globalmapper.com -
Thank you, Mike...I understand the projection distortion. Does the GM scale bar always default to a great circle? Is it, or will it be, possible to show and X & Y scale bar to assist and show the map distortion?
Thanks again and keep up the good work.
-Chuck -
Chuck,
The scale bar is based on the Y direction scale as that tends to be much less distorted in most projections. Note that a perfectly correct scale bar isn't possible for any 2D view of the earth as the actual true scale will vary depending on where you are on the map, so the scale say at the bottom of your map won't necessarily be the same as the scale at the top, especially if a large area is covered. The best you can do is use a projected system appropriate for your area to minimize distortion.
Thanks,
Mike
Global Mapper Support
support@globalmapper.com
Categories
- 12.7K All Categories
- 5.6K Features Discussion
- 342 Downloading Imagery
- 1.3K Elevation Data
- 380 Georeferencing Imagery Discussion
- 628 GM Script Language
- 53 User Scripts
- 113 GPS Features
- 414 Projection Questions
- 819 Raster Data
- 1.3K Vector Data
- 6.6K Support
- 177 Announcement and News
- 908 Bug Report
- 558 SDK
- 1.2K Suggestion Box
- 3.7K Technical Support
- 562 Other Discussion
- 129 GIS Data Sources
- 27 Global Mapper Showcase
- 233 How I use Global Mapper
- 107 Global Mapper Forum Website