# 20040202: Drawing circles or arcs as part of map boundaries

• Subject: 20040202: Drawing circles or arcs as part of map boundaries
• Date: Mon, 02 Feb 2004 15:16:51 +0930
• >from: Karen Pon <k.pon@bom.gov.au>
• >keywords: 200402020551.i125pap1024592
• >organization: UCAR/Unidata

`Hi`

Is there a way to draw circles or arcs when creating maps in McIDAS? At the moment I'm plotting approximate lat/lons.

```Thanks,
Karen```

Karen Pon
Defence Meteorological Support Unit
Ph: (08) 8920 3860
Fax: (08) 8920 3861

```Date: Mon, 02 Feb 2004 08:57:38 -0600

`I'm not sure what you're trying to do, but....`

```If you have a set of points in the x,y plane that is your frame,
you can draw a line through them.  If those points define a circle
or arc, then you draw a circle or arc.```

```There is no way to give the equation of a circle to the graphics
routine and have the graphics routine draw the circle -- you
have to compute the points on the circle.  The graphics routine
doesn't do that.```

```For your example, if you compute the longitude every .1 degree
along a latitude circle, and draw a line through those points,
you'll get an arc-like line.```

`I hope that's a clear explanation.`

`Scott`

```Date: Mon, 02 Feb 2004 09:37:01 -0600

The DIST command allow you to draw circles and the CIRCLE command (in Mc-XRD) allow you to draw arcs.

`Rick`

From: "HOETH, BRIAN R. (JSC-ZS) (LM)" <address@hidden>
Subject: RE: Drawing circles or arcs as part of map boundaries
Date: Mon, 2 Feb 2004 12:01:27 -0600

`Hello,`

awhile back too? Is there a way to make a circle AND create a McIDAS map
file from this circle? Someone here created a "quick and dirty" program
that will make a 5 nautical mile circle around the Johnson Space Center and
then create a McIDAS map file for this circle. The program is hard-coded to
work only for JSC's lat/lon and would obviously be more useful if it were
able to handle lat/lon and maybe a radius as input.

```Anyways, I've attached the program.  It's a very small C program that you
can run from a unix environment.  Hope this helps and let me know if you end
up modifying it to use keywords!```

```Brian Hoeth
Spaceflight Meteorology Group
Johnson Space Center, Houston, TX
Office:  281-483-3246
Operations:  281-483-1051```

```Date: Thu, 05 Feb 2004 21:46:12 +0930
Subject: RE: Drawing circles or arcs as part of map boundaries```

`Hi`

`Thanks for all of your suggestions.  I'll try out various options.`

`Karen`

```From: Russ Dengel <address@hidden>
Date: Tue, 10 Feb 2004 08:15:29 -0600```

Just to add my \$0.02 on this topic. The CIRCLE command in McIDAS XRD does all of this and more. It will plot radial distances from any Earth location (lat/lon, WMO station, world city, or current cursor). It can display radials at any distance with labeled bearing markers, and for certain satellite projections, display parallax shift to a specified height above the surface.

It has a comprehensive set of plotting controls for color, dashing, line width and labeling.

`Russell Dengel`

```From: "HOETH, BRIAN R. (JSC-ZS) (LM)" <address@hidden>
Date: Thu, 12 Feb 2004 09:43:24 -0600```

`Russ,`

```But does the CIRCLE command have the functionality to save the circle drawn
as a MAP file?```

`Brian`

```From: Russ Dengel <address@hidden>
Date: Thu, 12 Feb 2004 10:07:17 -0600```

No, the Earth to frame projection computations are performed by CIRCLE. Since MAP does basically the same thing (converts Lat/Lon to frame coordinates) I never inserted the option to save the results to a MAP file. This allows the user to adjust the scaling based on image resolution and allows CIRCLE to adjust placement of labels. MAP contains no concept of radial labeling.

`    Russ`

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