Working with Large Maps

In this example we overlay a traverse on a digital base map (e.g. TRIM map). This is often useful for presentation purposes. The following steps outline the process. 

1. Get a DXF file covering the area of interest from your map provider (GIS department). When requesting DXF data, be sure to keep the area of interest as small as possible and include only the themes (roads, properties etc.) you will need in your final map product. This will speed up processing considerably.

2. Import the DXF file into the Terrain module using menu File - Import - DXF Import File.

3. After the file has been loaded you should see the features in the Plan window. If you don't see any features, press the TAB key to cause the program to advance to next feature and automatically scroll it to the center.

 

Figure: Imported Map Features

Tips for improving display speed

Large map files can be awkward to work with because of their slow screen redraw speed. Here is several ways to speed things up.

 -Turning off Label display in the View - Plan Options menu can speed up the display by a factor of 3.

-Use the Escape key when the cursor is in the Plan window to stop drawing. This will allow you to select menus etc. without waiting for the screen drawing to complete.

-Turn off the display of all features except those which are required. You can turn them back on prior to output. We will illustrate this in the next step.

4. It is common for DXF files to save map themes on different layers. E.g. Roads in one layer, property boundaries in another etc. If a layering scheme has been used, it is very easy to turn off the display of all features in a layer. To see if the DXF file has layering click on a feature to select it and look at its name (displayed in the lower right corner of the screen). If the file has layering, the feature name will be the layer name followed by the sub-id number. In our file, all contours are in the form 37-xxx where 37 is the contour layer and xxx is the sub-id. 

Figure: Contour layer is indicated by a 37 prefix in each contour feature

5. To turn off the display of all contours, select menu Edit - Select Features by Name - then click on Un-Select All - choose Advanced. Choose matching name 37<space> and press the Select button. Press OK and then select menu Edit - Modify Selected Features - Properties. Turn off the display property. Save the terrain file.  

Figure: Select Features by Name Dialog box.

6. Determine the x,y coordinate on the map corresponding to the POC of the traverse. NOTE: When you move the cursor in the Plan Window, the x,y coordinate location is reported in the lower right hand corner of the screen. This step may not be necessary if you have the UTM coordinate from a GPS device.

7. Using the coordinate obtained in step 6 , set the start station coordinate of the traverse in the Survey/Map module. Save the traverse and import it into the terrain file with the map. The traverse should appear in the correct location.

Figure: Traverse Overlayed on the Base Map

 NOTE: If there are other tie points on the on map you can also adjust the traverse at these points. To do this determine the map coordinate using the mouse (as described above) and once again set the traverse station coordinate in the Survey/Map module. Obviously this adjustment may adversely effect the accuracy of the surveyed traverse.