With OCAD and GPS you always know where you are
You can use GPS (a world wide system of positioning satellites)
in different ways:
-
Connect the GPS receiver to your tablet PC or notebook.
Your current position will be displayed on the map.
- Collect points in the terrain with your GPS receiver
and transfer them later to your PC. You need a PC program which
can read these points from the GPS receiver and export them
as a DXF file (wich can be imported in OCAD) or a BMP file
(which can be opened as a template in OCAD).
GPS Receiver Connected to a Tablet PC or Notebook:
The GPS receiver is connected to the serial port of the pen computer or notebook.
In OCAD a pointer displays the current position on the map.
OCAD has no automatic recording of the position, it just displays the current position.
The GPS receiver sends its data in the NMEA 0183 format.
This format is supported by allmost all available GPS receivers.
(NMEA stands for National Marine Electronics Association).
If DGPS (Differential GPS) is used then the DGPS receiver is
connected to the GPS receiver and has no direct connection to the pen computer.
Coordinate Transformation:
The GPS receiver sends coordinates in the WGS84 coordinate system.
To translate these coordinates to the local coordinates a pragmatic
approach has been taken. On known points of the basemap (like street crossings)
the GPS coordinates are adjusted. That means you have to go to
these adjustment points with the equipment. Up to 12 points can be used
and the resulting transformation is an Affin Transformation which fits best with the adjustment points.
Collecting Data with the GPS Receiver Alone:
You can collect data with the GPS receiver alone. Many GPS receivers have storage for storing points and lines.
After fieldworking the area, the GPS receiver is connected to the PC and the
GPS data is transferred. OCAD cannot read the GPS data
directly. Instead you have the following alternatives:
- For most receivers you can get a PC program to do the transfer.
Some of these programs can produce a DXF file which can be imported
in OCAD. Other programs can export a BMP file which can be opened as a template in OCAD.
-
There are some programs which can read data from many popular GPS receivers. They can
export a BMP file which can be opened as a template in OCAD.
These are their home pages:
GPSTrack
OziExplorer.
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