gridding in ilwis
DESCRIPTION
Method for creating a local coordinate system and gridding on a specified distance using the ILWIS software.TRANSCRIPT
Import the scanned image of toposheet into ILWIS using GDAL
Open the maplist
It will be shown as a maplist
As you can see there are no latitude and longitudes, only pixel rows and columns
Now create a georeference (tie points)
with coordinate system unknown or any other name
Give the SW corner of toposheet x=0 and y=0
The SE corner is x=length of toposheet in mm x 50 (1mm=50m for toposheet scale)And y=0
Likewise NE corner is x=length of toposheet in mm x 50 And
Y= height of toposheet in mm x 50
And similarly for the NW cornerNow the toposheet is registered with the local (false) coordinates
Now create a segment map
Just the outer boundary of the map
Remove the segment map layer
Open the segment map separately
Create a coordinate system
Give any name
Select coordinate system tie points
And related coordinate system latlongwgs84
Select yes
Give the lat long of all four corners
Now you can see that we have both the local false coordinates and
the lat long on wgs 84 as well.
Now right click on the coordinate system created in the previous stepsAnd
Select create georeference
Give any nameSelected georef tie points
AndSelect the toposheet as the background map
Enter the coordinates of all four cornersUse the local coordinates calculated previously
Notice that there are no coordinates calculated
Notice that we now have both the local coordinate as well as the lat long
Exit the editor
And go to layersAdd grid lines
Give grid distance of 1000 m
The gridding is done
And as you can see it starts from the SW corner precisely
And the smaller cells on the eastern and northern margins are preserved
However if you want this grid as shape file then it needs to be digitized (which takes about half an hour)
For transferring way points to GPS
Download the GPS trackmaker software. It is free
If you have selected points in ILWIS I suggest making point map of all those points and exporting this point map as shape file with WGS 84 coordinate
system.
Open this shape file in GPS trackmaker and transfer the points to GPS as way points.
If you have selected points on GOOGLE EARTH then put all the points in one folder and save it as a *.kml/kmz file of that folder
And thenOpen the .kml file in GSP trackmaker and transfer the data to GPS.