Gridding in Ilwis

Post on 28-Nov-2015

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Method for creating a local coordinate system and gridding on a specified distance using the ILWIS software.

Transcript of Gridding in Ilwis

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.