Tech Tips


Project Settings

Due to some confusion regarding the set up of a new project, here is a guide to the settings that can be made:
 

TechTips


Starting a New Project

You must be in one of the Design Modules, i.e. Terrain, Roads etc. if you are creating a new Terrain File, then you need to be in Survey Mode. To change Modes click on the Applications Menu.

File Menu > Project Settings



The top half of the dialog is related to the specific data items that can be included in a project while the bottom half of the dialog is related to the projection settings that need to be made in order to correctly display some of the project items. Currently only Terrain data really requires locale settings (other than the Hemisphere settings) but you must set it at the start of a project in case extra data items are added at a later stage.

Item Settings
In order to include any of the available data items in the project simply click on the checkbox after the name of that item. This will automatically open a standard File Open dialog where you can specify the name of a new data file, or select an existing data file that must be included in the project. In the case of a Drawing item however, you may only select existing drawings.

Once you have specified the name of the data file to be included in the project you can use the Browse button next to the file name to change the name of the data file to be used.

If you change your mind about including a certain data item, simply click on the checkbox next to the item again in order to uncheck it. This will then remove that data item from the project.

Project Title
In this field you can enter a title for the project that will be displayed at the top of printouts. This can help you identify the source of printouts at a later stage.

Projection Settings
This is the area where most people are having problems so some detail is warranted.

You must make the settings that determine the manner in which the stored coordinates are projected onto the display surface (the Design Centre window).

Once a data item is selected in the top half of the dialog, the Locale settings area becomes available.

Hemisphere
Select either Southern or Northern hemisphere. In the absence of a drawing as one of the project items this setting will govern the display of coordinate values. Note that Southern hemisphere denotes projects located below the Equator while Northern hemisphere denotes projects located above the Equator.

Projection
There are 4 choices that can be made here. These are Local, Transverse Mercator, UTM (Universal Transverse Mercator) and New Zeeland Transverse Mercator

Local
Selecting this option will automatically set the Datum, Origin latitude, Scale factor, False Easting and False Northing. In this projection entered coordinates are stored as-is with no conversions applied. This is the same format as was used in Stardust version 5.x and prior versions. The only other setting that needs to be made is the Prime longitude.

Transverse Mercator
This is the projection used in South Africa. It is defined as a 2 degree panel around the specified Prime longitude. For this projection you will also need to specify the Datum, Prime longitude and Origin latitude. In this projection coordinates are stored as geographical coordinates and converted between LO and Geographical as and when needed.

UTM
This projection is used in various African countries. It is defined as a 6 degree panel around the specified Prime longitude. For this projection you will also need to specify the Datum, Prime longitude, Origin latitude, Scale factor, False Easting and False Northing. As in the Transverse Mercator projection, coordinates are stored as geographical coordinates and converted between LO and Geographical as and when needed.

Note that UTM is normally defined by a block number. In order to determine the Prime longitude of a UTM block number simply carry out the following calculation:

(BLOCKNUMBER x 6) - 183

This will give the Prime longitude in degrees.

Datum
This determines the ellipsoid on which the projection is based and therefore the constants used for the mapping projection. Note that the Cape datum is the equivalent datum to that used by Stardust and that South Africa has recently (January 2001) converted to using the WGS 1984 datum.

Central longitude
This is the central longitude (LO) of the panel in which the data falls (actually the longitude on which the 0 value of the horizontal ordinates of the coordinate system falls) and is ALWAYS an odd value i.e. 19, 21, 31, etc. You must also select whether this LO is East or West of 0 longitude (Greenwich).





Clicking on the Advance button brings up additional settings.



Origin latitude
This is the latitude on which the 0 value of the vertical ordinates of the coordinate system falls and it must also be specified whether this latitude is North or South of 0 latitude (the Equator). This should be set to 0 (origin at the equator where North or South are immaterial) as all of the projections we currently use have their 0 vertical coordinate at the Equator.

Scale factor (Applies to UTM projection only)
This is the factor by which coordinates are adjusted in order to fit the projection. The specified factor for UTM coordinates is 0.9996 and this should only be changed in exceptional circumstances and then only after approval by a knowledgeable authority on projections.

False Easting (Applies to UTM projection only)
This is a coordinate correction applied to horizontal ordinates. The specified value for UTM coordinates is +500 000, and this should only be changed in exceptional circumstances and then only after approval by a knowledgeable authority on projections.

False Northing (Applies to UTM projection only)
This is a coordinate correction applied to vertical ordinates. The specified value for UTM coordinates is 0 for Northern hemisphere projects and +10 000 000 for Southern hemisphere projects, and this should only be changed in exceptional circumstances and then only after approval by a knowledgeable authority on projections.

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