The Benefon ESC! Mapping Tool
Questions & Answers
A. Here are some solutions:
A. The following table summarises the Spitfire's functional differences with and without a licence.
A. Files named with a .gri extension are Geo Raster Images. This is Spitfire's native map format and contains the following information:
Note: The evaluation version can only read georaster image files, you will need to purchase a licence in order to create them.
A. Files named with a .tsl extension are Spitfire tile selections. These are the files you create when you choose save from Spitfire's File menu and contain the following information.
Note: If you move or rename the map image or .gri file after creating a tile selection you will be prompted to browse for the file when you next open the selection.
A. Files named with a .wld extension contain the geo data required to correctly relate the map image to a geographical position. The .wld must be placed in the same folder as the associated map image and must also have the same file name (apart from the differing extension). Creation of the .wld files occurs when you georeference a map image by chosing "Georeference Map" from Spitfire's File menu.
The .wld file is a simple 6 line text file that contains the following information:
In Spitire version 2 the format of the .wld file has changed to support multi-point georeferencing and contains the map projection and parameters, the tie point information entered when the map was georeferenced, and the associated datums.
A. To the ESC! handset a map consists of a collection of map tiles, each tile being a 240 x 240 pixel square of map image. There is no requirement for the tiles to be adjacent to each other, thus enabling you to select just the parts of the map image that you require.
Adjusting the size of Spitfire's selection grid will cause Spitfire to reduced the image resolution of each tile in order to maintain the 240 x 240 pixel tile size, this allows you to squeeze a larger area of map into your handset.
A. The primary map layer controls the scaling of the other map layers in order to maintan the correct positioning and size. For example if a large scale map is the primary layer a small scale map layer's pixel size will be reduced so it can be correctly placed over it. Conversely if a small scale map is the primary layer a large scale map layer's pixel size will be expanded. Normally the scales of each layer will be similar and the difference in pixel size will not be noticeable.
By default the primary layer will be the first map loaded into Spitfire, but this can be changed from the layers dialog, which can be found on the view menu or by pressing the button.
A. The layer order can be changed from the layers dialog, which can be found on the view menu or by pressing the button. Select the layer you wish to move then click on the Up or Dn buttons on the right to move the layer up or down.
A. Georeferencing is the term used to describe the act of placing geographical coordinates onto a map image. This enables Spitfire and your Benefon ESC! handset to relate a latitude and longitude to the correct position on the map image.
A. You can express latitude and longitude coordinates in decimal or DMS (degrees, minutes, and seconds) format.
DMS coordinates can be entered in any of the following ways, where D is a single letter that indicates direction (N for north, S for south, E for east, or W for west):
If you are entering a coordinate and the location is south of the equator or west of the Prime Meridian in Greenwich, England, express the latitude or longitude as a negative value; for example, -15.75 degrees latitude and -64.25 degrees longitude.
A. Open the map image file using the file -> open menu item. Ensure that the image resides on writeable media as the georeference data is saved in a file in the same location. Press the georeference map button to start the georeference dialog.
First you should select the map projection from the drop down list, the map projection is the means by which the curved earth surface is mapped to a flat plane. The Benefon ESC! requires that it's maps are flattend in such a way that there is a linear increase in latitude as you move from the bottom edge to the top, and similarly a linear increase as longitude as you move from the left edge to the right. If your map image is already projected in this manner you should choose the Latitude/Longitude projection. Otherwise you should choose the projection that matches the map image. Choosing the correct projection is important, but can be difficult especially if it is not written on the map somewhere. As a first guess you should probably try the Transverse Mercator projection as this is most commonly used. After selecting the projection you should click on the setup button, to set the correct parameters for the projection. Spitfire knows the correct parameters for most common grid systems, so you should be able to select the grid system for your map from the drop down preset list. For example, for a British Ordnance Survey map you should choose the Transverse Mercator projection and choose British National Grid from the preset list.
If you really can't determine which map projection to use you could try use the "Polynomial Fit" feature. Select Latitude/Longitude from the projection list, then select "2nd Order" from the Polynomial fitting list. Using this method you will need to enter at least 6 lat/long tie points, Spitfire will then reproject the map image using a polynomial equation derived from the entered tie points.
Different areas of the world use different mathematical models of the Earths shape, this mathematical model is called an ellipsoid. A given latitude and longitude on one ellipsoid may refer to a completely different position on another. A datum specifies the origin of the latitude and longitude values and also the reference ellipsoid. Spitfire allows you to choose two datums during the georeferencing process the first is on the projection setup dialog, this datum is used in the conversion between grid reference values, specified as northings and eastings, and latitude and longitude. The second datum you only need to specify if you are entering your georeference points as latitude/longitude values. This datum is set on the main georeferencing dialog when you have selected latitude/longitude as the georeference point type, and applies to all latitude/longitude value you enter. During the reprojection process all latitude/longitude values need to be converted to northings and eastings so the projection datum must be set correctly even if you are only specifying your georeference points in terms of latitude and longitude.
You should now enter a minimum of two georeference (tie) points, each georeference point ties a geographical position to a specified pixel on the map image. It is preferable to specify more than two georeference points, especially if you have scanned a paper map. Three points will correct any rotation, and four or more points will correct rotation and skew. The algorithms employed attempt to find the best fit translation for the given points, you may therefore find that entering more points improves the accuracy over the whole map. In general you should attempt to place the georeference points as far apart as possible, one on each corner for example, however you should avoid the edges if you are georeferencing a scanned paper map as this is where most distortions will lie. You should also ensure that all the points are not aligned in either horizontal or vertical directions.
To enter the georeference points click on the map to place the point marker at the required position, the position can be adjusted with the cursor keys holding the shift key to move in larger steps. The pixel position is automatically transferred to the form on the georeference dialog. When you are happy with the position enter either the corresponding latitude and longitude or change the point type to northings and eastings and enter the grid position. Click on the "add" button to add the points to the list.
To change a georeference point, click on the list item of the point to be modified, it's values are automatically transferred the form. Update the values as appropriate then press the "update" button, the form values will replace the values of the selected list item. Press the "goto" button to bring the XY position on the form into view, alternatively double click on a list entry.
When you have added all the points into the list, press the "Save" button to create the .wld file which will be written to the same directory as the bitmap image. The map reprojection will begin and the georeference dialog will close when complete. The reprojection can take a little time on slow machines and must be performed each time the map is loaded. To avoid this delay the reprojected map can be saved as a native Spitfire .gri file (registered version only), the .gri file is self contained so the original bitmap and .wld files are no longer needed to use the map. However you cannot change the georeferencing in a .gri file you must use the original bitmap image and .wld files.
A. The information calculated when you georeference a map image is saved to a small text file with the same name as the map image but with a .wld file extension. In order for Spitfire to find this geo data when the map image file is later opened it must reside in the same folder. Ensure that your disk is not full and that the media is writeable. If for example you are trying to georeference an image that is on a CD-ROM, copy it to your hard disk first.
A. The map you are using is a Spitfire georaster image (.gri) file which is already georeferenced and reprojected and thus cannot be georeferenced again.
A. You cannot adjust the grid size until you enter grid edit mode by pressing the button on the toolbar.
A. You cannot enter grid edit mode while you have tiles selected. You must deselect all the tiles first using the toolbar button.
A. First of all you must have a georeferenced map image loaded into Spitfire, you must also ensure you have no tiles selected. Press the button on the toolbar, this will put Spitfire in grid edit mode. To change the grid origin click the and drag the mouse cursor on the map image, you can also use the cursor keys, with and without the shift key to move the origin if you prefer. To change the size of the grid square use the slider control in the toolbar or use the page up and page down keys, again with and without the shift key. When you are satisfied press the button again to leave grid edit mode. When you save your tile selection the grid settings are also saved, ready for the next time.
A. There are several ways of repositioning the map image:
A. You can change the zoom level by using any of the following methods:
A. First make sure that the selection grid is enabled by pressing the button on the tool bar. Then you may select and deselect tiles using the mouse as follows:
Whether a tile will be selected or deselected depends on the state of the tile where you initially click the mouse. If the initial tile is not selected you will begin to select tiles and vice versa.
A. Right clicking on the overview window brings up a context menu that can be used to change the window size.
A. Right clicking on the Lat/Long display brings up a context menu that can be used to choose between decimal degrees, degrees and minutes or degrees, minutes and seconds.
A. The latitude and longitude values displayed in the status bar are aways within the WGS84 datum.
A. Hold down the shift key while you move the mouse.
A. Because of the way the Benefon ESC! manages it's memory it is not possible to accurately predict the memory available after maps have been deleted. The solution is to delete all maps from the handset to defragment it's memory, then load all the maps again. Alternatively you could reduce the selection by a tile or two, however don't forget to delete the partially transferred map from the handset first.
A. There appears to be a bug the the handsets firmware which occasionally causes it to crash. The bug seems to be provoked by the order in which a particular selection of tiles are transferred, so retrying the transfer often fails in exactly the same way. The handset may sometimes get so confused that it will no longer respond to the keypad or even the power button and it may be necessary to remove and replace the battery to in order to recover.
There are two possible solutions that may resolve the problem:
A. There appears to be a bug in the handsets firmware which causes it not to respond fully when commands are sent to it too fast. Spitfire will automatically adjust the rate at which it sends commands to the handset when this error occurs. So keep retrying until eventually Spitfire finds the optimum rate for error free communications. Spitfire will then remember this and use it for all future handset communications.
A. The default map scale is calculated from the dots per inch (DPI) value saved in the image file combined with the geo data added by georeferencing the image.
A. All common bitmap image file formats store the image size in terms of DPI, width in pixels and height in pixels and not in units of measurement such as inches or meters.
A. Using an example of a 1:50000 scale map on which 4000 pixels represents 20km on the ground.