Category Archives: OCAD 12

Declination / Rotate Map

Declination – Background Information

Magnetic meridians. Source: Wikipedia.

Does a compass point to the geographic North Pole? No. Does a compass point directly to the magnetic North Pole? Not necessarily.
The compass is always oriented in the direction of the local magnetic meridians and therefore usually shows neither exactly to the geographic nor straight to the magnetic North Pole. The Declination is defined as the angle between the direction of the magnetic meridians and the direction to the geographic North Pole at the observation site.
If magnetic north lies west of geographical north, the declination is called western and counts as negative; if magnetic north lies east of geographical north, the declination is called eastern and counts as positive.
An observer in middle and northern Europe sees the Arctic magnetic pole to the west of the geographical North Pole. At the same time, however, he notes that the local magnetic meridians are pointing in a direction just east of the geographical pole, so that the declination here is a few degrees east.

World Magnetic Model. Source: NOAA.

Declination varies both from place to place and with the passage of time. The reason for this are complex fluid motions in the outer core of the Earth which cause the magnetic field to change slowly with time. That’s why old maps have to be adjusted to the new declination time by time.
The declination in Switzerland is currently only around 2° and is therefore neglected in almost every map. 1° difference would mean 2.2m deviation for 100m. In the example below, you should miss the control by about 13m on the right (purple x)  when running straight with your compass ( 2.1° declination, 280m distance).

How can you adjust the Declination in OCAD?

In OCAD, there’s a new function called Rotate Map to Magnetic North.
This function considers the Magnetic declination and the Grid convergence of your current position and suggests by how much the map should be rotated. Learn more about this new function here.

In the Map Menu, there are two more functions where you could rotate your map. Do not edit the Angle in the function Set Scale and Coordinate System. Only change the angle there, if you start a new map and haven’t drawn any objects yet. The function Rotate Map is basically the same as Rotate Map to Magnetic North, but not that sophisticated.

Things to consider

Every time you rotate the map, the position accuracy of your objects is reduced a bit due to rounding differences. Therefore, we recommend not to adjust your map every year to the current declination, but maybe every fifth year.

A possible workflow would also be to rotate the map only before you print and export it. This way, you avoid rounding errors. The disadvantage is, that if you rotate the map at once with a big angle, non-rotated objects oriented to north could possible suddenly interact with rotated objects in a negative manner. Therefore, we do not recommend this workflow.

Remove Overshoots and Undershoots

Overshoots and Undershoots happen when your drawn line doesn’t connect exactly with the neighboring line it should intersect with. Mostly, the error only becomes visible with a large zoom level.
In OCAD, there is a function that removes Over- and Undershoots of selected lines. If you want to prevent Over- and Undershoots, enable the Snapping function.

Remove Overshoots and Undershoots

For an animation and more information, please see our Wiki.

 

Export Courses to KMZ

In the OCAD Course Setting module, you can export your courses as KMZ files and watch them later in Google Earth. KMZ files can contain both vector and raster objects.

Originally, this tool was developed for Trac Trac and their application O-Track. O-Track is a service which makes tracking, viewing and sharing orienteering easy and fun for both beginners and professionals.

This is how it works:

– Be sure your map is georeferenced and a coordinate system is set.

– Choose the Courses (KMZ) command from the Export submenu of the Course Setting menu.
– Select the desired extent and click on Export.

– Select which courses/classes shall be exported. Select multiple courses/classes by holding the
Ctrl key or click the Select all button to select all courses/classes. All courses/classes will be saved in the same KMZ file.

– Click on the exported KMZ file. Google Earth will start automatically. You will find a folder for each course in your Temporary Places with the course maps and all controls. A PNG file will be created for each course. The controls will be displayed by placemarks.

See also or Wiki for more information.

Run OCAD on Linux

OCAD is a Windows software. However, OCAD runs on Ubuntu using Wine.

We installed Wine on Ubuntu and run OCAD afterwards without any problems.

Wine is a free software and enables Linux users to run Windows applications without a copy of Microsoft Windows. Install Wine from the Ubuntu Software Center.

Create Smoothed Contours Using TPI

TPI stands for Topographic Position Index, which is defined as the difference between a central pixel and the mean of its surrounding cells. Choosing this option, OCAD first creates a smoothed DEM using TPI and calculates contours afterwards.

Some details may get lost, but results are very satisfying in constant slopes. Use these contours, if you want to adopt the calculated contour lines directly to your map.

In the DEM Wizard you can create “normal” custom contours (no smoothing) and/ or smoothed contours using TPI in one single step:

  • Choose the desired amount of contour and the interval.
  • Assign a line symbol for each type appears. By default, the first three line symbols in the settings are pre-selected.
  • Click on “Load symbols from template…” to get 12 line symbols at the bottom of your symbol box, which can be used for the settings.
  • Use different symbols for depression to distinguish depressions from hills.

As mentioned in the beginning, TPI contours were derived from a smoothed DEM, means some details will get lost. The following recommendations can be made:

  • For mapping in the terrain, use the custom contour lines as background, where you have all details on it.
  •  To draw contour lines on the PC, first calculate and load the TPI contours and adapt them afterwards where needed. Use the Reshape function for that.
    Especially in steep and constant slops, the biggest part of the TPI contours can be adopted to your map without redrawing. You gain much time like that.

For further information, please visit our Wiki.