Добавил:
Upload Опубликованный материал нарушает ваши авторские права? Сообщите нам.
Вуз: Предмет: Файл:
NavNet810_Manual.pdf
Скачиваний:
44
Добавлен:
02.05.2015
Размер:
3.44 Mб
Скачать

FAQ and Tips

Chapter 9

 

 

 

The local Cartesian coordinates of the origin also need to be defined in the Origin in Local Cartesian Coordinates box. While these coordinates are generally left at zero for most applications, you are free to change them.

Define the Orientation of the Grid

If the Y-axis is to be parallel to north at the origin, the rotation angle can generally be left at zero. Otherwise, click on the Compute button to calculate the rotation angle. In order to do so, coordinates must be known for a second point, which must lie along either of the horizontal axes. Enter these coordinates in the new window that opens under the Geographic Coordinates of a Second Point box. You must then specify on which axis the point lies, keeping in mind whether it is in the positive or negative direction.

Once the information has been entered, click the OK button. The program displays the calculated rotation angle of the grid, as well as the azimuth and distance between the two points. Click OK.

Define the Scale Factor

In the Local Cartesian Settings window, the computed rotation angle should now appear. The scale factor can be left at unity, or else it can be corrected such that spatial distances will agree with horizontal distance measurements. In such a case, the correction, s, can be calculated with the following equation:

s = R R+ h

In the above formula, R represents the radius of curvature of the Earth (~6371 km), while h is the height of the second point, also in kilometers.

Once you click the Finish button, the grid is defined and appears in the list of grids in the Define Grids window. This grid is now available for use in the Export Wizard so long as you select a profile containing the Selectable Grid variables. See Section 2.7.4, on Page 111 for more information.

9.8.6How do I define a local coordinate grid?

Localized systems can often be best reproduced in Waypoint’s software through the creation of a Local Definition File (LDF). These can be defined in advance via Tools | Grid/Map Projection | Define, or through the Export Wizard at the time of output by using any profile that contains the Local Plane variables. The following procedure assumes you have chosen to create the LDF file in advance.

Create a New Grid Definition

Select Tools | Grid/Map Projection | Define. The Define Grids window appears and displays a list of already existing grid definitions. Click the New button and give the grid an appropriate name. Select Local Coordinate Definition as the grid type. Click the Next button.

Select Transformation Parameters

From the Type drop-down menu in the Definition box, select the transformation that is required.

An error will occur during the computation if insufficient observations have been supplied for the selected transformation.

Next, specify the datum in which the geographic input coordinates will be supplied, as well as the units in which the grid coordinates are measured. Finally, select a grid upon which the program will base its computations. The default is a Transver Mercator projection where the central meridian and parallel represent the approximate center of the survey, which the software computes by averaging all points.

Enter Observations

To define the grid, add observations by clicking the Add button under the List of Stations box. The Add/Edit Local Station window appears.

GrafNav / GrafNet 8.10 User Guide Rev 4

281

Chapter 9

FAQ and Tips

 

 

If a station with known coordinates is already loaded in the project, you can enter its name in the Name of station field and click the Find Point button to load its coordinates. If the name of the point is unknown, you find it via the dropdown menu available under the Select from list of points in project option. Listed points include station or camera marks loaded from the STA file, or any known points that were loaded with user-provided latitude and longitude. You are also free to specify points from your Favourites. If the point does not already exist in the project or in the Favourites, define it here by providing a name and manually entering its coordinates.

Next, enter the coordinates of the point in the local grid system. If a coordinate for the point is unknown, be sure to disable the Valid option.

Compute the Transformation Parameters

Once all the observations have been entered, click the Compute button to allow the software to calculate the values of the unknown transformation parameters. An RMS fit of the transformation points will be computed. At this point, the transformation required to obtain positions in the local system will be completely defined. Click OK to save an LDF file to the installation directory. The Update button will replace existing station geographic coordinates with those currently loaded in the project.

With the transformation now defined, you can output your solution in the local system by running Export Wizard and selecting either the Local Coordinates profile, or any user-defined profile which contains the Local Plane variables. See Section 2.7.4, on Page 111 for additional information.

9.8.7How do I process an aerial survey with camera event marks?

Load Camera Event Marks

After adding the master and the remote, ensure that the camera event marks are loaded. For user logging position records, the camera event marks should be visible in the Mapping Window. If position records are not being logged at the remote, it is possible that these marks will not show up until after processing has been performed. However, if the marks fail to show after processing, they will have to be loaded manually via File | Load | Camera Event Marks. For instance, Ashtech (Thales) events must be loaded in this manner. See Section 2.3.10, on Page 41 for details.

Configure Processing Settings

Select Settings | Load Settings From | Airborne to utilize a parameter set that is well-suited for airborne data. While these options may not be perfect, they are an ideal place to start. If the base station data is interpolated, make sure the Only search on exact interval option is enabled and enter the original interval in the Search on data interval field. See on Page 100 for information.

Process and Analyze Data

After processing has completed, view the Combined Separation plot under Output | Plot GPS Data. The plot should, ideally, show a separation near zero. See Section 9.8.1, on Page 278 for further help analyzing the results.

Output Final Coordinates

When processing is done and the results are to your satisfaction, the final step is to output the solutions. To do this, use the Export Wizard, under the Output menu.

To obtain the coordinates for the camera marks, select the Features/Stations as the Source, and select an appropriate profile. See Section 2.7.4, on Page 111 for help creating a profile.

You will then be asked to enter the camera-to-antenna offset. This lever arm is used by Export Wizard to transfer the computed coordinates from the Kalman filter at the remote antenna to the camera.

The offset is defined in the local body system of the aircraft, and not the camera. The right-handed coordinate system is defined as follows:

X-axis positive axis through the front nose of the aircraft Y-axis positive axis through the left wing

Z-axis positive axis through the roof

282

GrafNav / GrafNet 8.10 User Guide Rev 4

Соседние файлы в предмете [НЕСОРТИРОВАННОЕ]