UTM Conversion to Lat/Long

Transcription

1 UTM Conversion to Lat/Long Introduction This procedure outlines steps to convert a list of coordinates into a Mapinfo table, then convert the projection and add columns to the table listing the Latitude/Longitude coordinates. Raw Data a list of UTM coordinates representing locations on the earth's surface Copy the data into a text editor (Notepad, Wordperfect, Word) and save as a plain text (*.txt) file. Run MapInfo. Choose File>Open Table... and select Delimited ASCII (*.txt) from the "Files of type" list. Navigate to the folder where you saved the list of coordinates in text format. Click 'Open'. You will be prompted "Delimited ASCII Information". Choose "Tab" as the delimiter and click "OK". 1 of 5 29/03/2000 4:07 PM

2 Your data will open in a MapInfo table with the UTM coordinates listed in separate columns. You will need to save this table under a new name in order to edit the table structure. Choose File>Save copy as... to make a copy of the original file. Choose File>Close all... to close all open tables and open the new copy you just created. Creating Points With the table open, choose Table>Create Points... The Create Points dialogue box appears. Choose an appropriate symbol and make sure the X and Y coordinates are being selected from the correct columns. From the table above, the following dialogue box reflects the appropriate entries. Click "OK". 2 of 5 29/03/2000 4:07 PM

3 As a general rule, the following chart defines Latitude/Longitude/UTM-X/UTM-Y coordinates for a region in southern Ontario. Latitude 43 degrees UTM-Y 4,763,000 metres Longitude -79 degrees UTM-X 623,000 metres NOTE: the default projection is "longitude/latitude". We are creating points based on UTM grid reference coordinates but the projection of the actual map will be in latitude and longitude. Keeping this default will enable us to establish precise latitude and longitude coordinates. If a map does not automatically appear, choose Window>New Map Window... to view the results. Opening a table from another database using the same projection and geographical coverage with confirm that your results are accurate. After opening a second table, choose Map>View Entire Layer... and choose all layers from the drop down menu. If your points don't overlap the other database, check the projection of the two tables to be sure they correspond. You may need to create the points over again. Clear Map Objects To begin again, you will need to delete the points you just created and re-save the table. In the Layer Control, make the table editable and click "OK". Choose Query>Select all from yourtablename... the points in the map window should be highlighted. Select Edit>Clear Map Objects Only This command will eliminate the points you created earlier. Choose File>Save table... to save the table as it was before you created points. You are now ready to repeat the create points operation. It is critical that you understand the relation between UTM-x/y coordinates and Lat/Long (see the table above for the 'general rule'). Adding Columns (fields) for Latitude/Longitude With the new table open (the one with points), select Table>Maintenance>Table structure... to add 2 new columns. Click on the "add field" button. Define the field name - "UTM_X"; data type decimal and a field width 6 and 2 decimal places. Add a second field with the same specifications and the field name "UTM_Y". Click "OK". Updating Columns using "Centroid" function Choose Table>Update Column... The following dialogue box will appear. Select the table and column to update. Under "Value" click the "Assist..." button. 3 of 5 29/03/2000 4:07 PM

4 After clicking the "Assist..." button, the following dialogue box appears: From the "Functions" drop down menu, select the "CentroidX" function. Click "OK". Click "OK" in the Update Column dialogue box. The results will appear in the browser showing the longitude in decimal degrees. Repeat the Update Column option to determine latitude as well. Your final browser should reflect similar values to the browser below. To convert the browser to a plain text file choose Table>Export and define the file type as Delimited ASCII (*.txt). Run a text editor to view this file. 4 of 5 29/03/2000 4:07 PM

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