Global Mapper Pro

Distance/Bearing/COGO Tool Creating Line with Different Bearing then Entered

BrianZ111
BrianZ111 Global Mapper UserTrusted User
edited November 2014 in Bug Report
I'm trying to create a line with a specific bearing and distance: 0.0173484° at 4096 meters. I am using the lower right corner of another shape as a reference for the starting point. I enter my distance and bearing and add the point.

Distance Bearing Dialog.gif

When I get to the feature dialog box it shows a different bearing: 0.0173524°

Feature.gif

After proceeding to create it I used the measure tool and confirmed it is not the bearing I set.

Measure.gif

Is this a bug or am I doing something wrong/misunderstanding how to use this tool?
I've tried a bunch of other bearings and from different start locations and they seem fine, it just doesn't like this for some reason.

Here's the Global Mapper workspace file if you wish to try to recreate it: Distance Bearing Line.gmw

Thanks for any help.

Comments

  • BrianZ111
    BrianZ111 Global Mapper User Trusted User
    edited November 2014
    Actually it doesn't seem to be exact for any bearings I pick now. Not sure what I was doing different before that it was.
  • BrianZ111
    BrianZ111 Global Mapper User Trusted User
    edited November 2014
    Did some more testing and it looks like it may have to do with whether I have the measure tool set to great circle or rhumb line. Looks a lot better when I set it to great circle although still slightly off. Is this setting supposed to affect the COGO tool?
  • bmg_bob
    bmg_bob Global Mapper Programmer
    edited November 2014
    Hello,

    The setting in the Measure tool does affect calculations in other parts of the program. When you create a line using the COGO tool, Global Mapper calculates the Bearing attribute value from the points in the line, and this calculation takes the Measure tool settings into account. If you want to recalculate the bearing attribute, you can:
    1. Click the Measure tool button
    2. Right-click on the map and select the measurement option (Great Circle, Rhumb Line, etc.)
    3. Click the Digitizer button
    4. Select the feature(s)
    5. Right-click and choose Analysis/Measurement->MEASURE - Display Feature Measurements...
    6. This will update the measurement attributes for the selected feature(s)
    Cheers,

    Bob
  • BrianZ111
    BrianZ111 Global Mapper User Trusted User
    edited November 2014
    OK thanks, I was switching between them a lot. I see I have to be more careful about that. However even when I have it set to great circle it is .0000001° different...0.0173483° instead of the 0.0173484° I enter. Why the difference, rounding error because it's such a small difference?
  • bmg_bob
    bmg_bob Global Mapper Programmer
    edited November 2014
    Hi,

    Yes, that is due to rounding error. The Bearing attribute value is calculated using the start and end points from the line, and is then converted to a string for display. The calculated bearing has greater precision than both the original input data and the output string, so either of these operations could introduce a slight rounding error.

    Cheers,

    Bob
  • BrianZ111
    BrianZ111 Global Mapper User Trusted User
    edited November 2014
    OK, thanks for the explanation.
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