Azimuthal extruded globe Parameters

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JBDesign
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Joined: Thu Aug 15, 2013 11:11 am

Azimuthal extruded globe Parameters

Post by JBDesign » Thu Aug 15, 2013 11:30 am

I'm working within the demo version and I'm a newbee at designing globes for a plastics manufacturer. I'm specifying the Azimuthal extruded globe for my projection, which appears to distort the land masses correctly, however the graticule is not correct, as I've been told by the globe manufacturer. The latitude lines are closer together at the equator and the manufacturer is saying they should be closer together at the pole. I see from the manual you can change the parameters. Will this just effect the graticule? The parameters go in increments of 10 from 80-0 in the demo, but the manual goes from 85-0 in increments of 5. Can anyone comment?

daan
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Re: Azimuthal extruded globe Parameters

Post by daan » Sat Aug 17, 2013 2:04 pm

Hello JBDesign, and welcome to the forum.

Geocart 3.1 has 5° increments for the extruded globe.

The graticule and land are integral. It does not make sense to shift the graticule against the land; that would give different coordinates for land than they actually have. If the spacing is incorrect, then it means that the land is also incorrect. You will find that spacing the graticule correctly results in proper land shapes as well. Things look right to the eye even with a fair amount of distortion, so it is no surprise that the land masses appear more or less correct even if they are not.

Does that help? Good luck with your globe!

— daan

JBDesign
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Joined: Thu Aug 15, 2013 11:11 am

Re: Azimuthal extruded globe Parameters

Post by JBDesign » Mon Aug 19, 2013 5:31 am

Thank you daan,

I realized the two were integral shortly after I left my previous posting. So yes, my land masses are incorrect as well. I understand changing the data in the parameters window distorts the graticule and land masses, but what I'm still unsure of is what figures to enter to change the distortion so it is correct. Page B82 in the manual lists the parameters from Radius 85° (any scale, any units), then 80° (same scale and units as 85°) thru the radius of the equator (same scale and units as 85°). What does this mean? My initial interpretation of that was to apply the difference between the 0° and 10° figures to the 90° and 80° figures and so on. Basically reversing the scale of the graticule proportionately so that the parallels were closer near the pole and farther apart at the equator.

My demo version of Geocart has timed out so I'm going to purchase the 3.1version for mac.

Jesse

daan
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Re: Azimuthal extruded globe Parameters

Post by daan » Mon Aug 19, 2013 11:22 pm

Hello Jesse,

The meaning of the explanation in the parameters is that you just use the same unit of measurement for all your measurements. For example, if you measure 28mm from the north pole to 85°N, then fine, enter 28 for that value, but then also use millimeters for all your measurements. You can use inches if you want, or furlongs, or anything else, as long as you’re consistent. Geocart doesn’t need to know what the unit of measurement is and doesn’t care.

The reason you have to set those parameters at all is because the globe extrusion process differs from manufacturer to manufacturer and even changes within a manufacturer sometimes. The manufacturer should tell you what those measurements are, or at the very least should give you a flat sample with parallels marked that they know extrudes to the proper distances between parallels on the globe. It’s nothing you could know yourself or that Geocart could know.

You can infer how parallels should be spaced if you have the manufacturer extrude a sample whose parallels start out equally spaced. In the extruded sample you would measure how much and in which direction each parallel moved. In Geocart you would set the opposite of those movements for each measurement in the dialog box. That may only be approximate, though; you might have to go through a couple of iterations to get it precise enough.

Does that help?

— daan

JBDesign
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Joined: Thu Aug 15, 2013 11:11 am

Re: Azimuthal extruded globe Parameters

Post by JBDesign » Tue Aug 20, 2013 12:46 pm

Thanks again daan, yes this helps.

Jesse

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