[GRASS5] How to register map

Eric G. Miller egm2 at jps.net
Thu Dec 20 02:00:06 EST 2001

On 20 Dec 2001 06:21:46 -0000, "kapil  tandon" <grass_team at rediffmail.com> wrote:

> Hi Everybody,
>              Well i am kapil tandon and i am new to grass
> i had worked a bit over it and i am stuck when you have to digitize a big map

Please direct future GRASS usage questions to the general user list.  In theory,
this list is more a communication channel for developers. See the webpage for
how to subscribe to GRASSLIST at baylor.edu.

> Well My Prob Is
> Prob1.I am trying to open a parts of big map scanned seperately.Though i am able to open them as a backdrop and digitize over them but when i view them all they overlap.I know this is because my backdrop maps were not registered.Even if u use v.digit it give u the facility to register ur map but only when u r using a digitizer as a degitizing device, i am using mouse. So that option is not available for me.

Okay.  These are scanned maps?  They have registration marks, coordinates?  Why not
register the maps?  Then digitizing over them will result in correct coordinates.
See i.points, i.vpoints, i.rectify, etc...  Presumably you'd only want to do a first
order transformation, so you'd only need three registration points per image
(though it might be better to use more, so root-mean square error checking can
help guide you to choose the best points).

> a) How can we register map when we use mouse as digitizing device.

First part is to have a LOCATION with a coordinate system other than simple x-y.
Second part is to digitize relative to that coordinate system, which means you
want your base maps registered first.  You can transform the vectors later, but
I'd assert that it'll be easier and you'll get better results if you transform
the source maps first.

> b) Can i open more then one backdrop adjacent to each other by using d.rast if yes how.It open but overlap but i want them to open adjacent to each other.Same prob is with vector files also
> _________________
> |       |        |
> |       |        |
> |  A1   |  A2    |
> |       |        |
> |       |        | 
> ------------------
> i hope my question is clear
> please find a answere for me i ll be really thankful

v.digit doesn't currently provide a mechanism for specifying more than one
raster and one vector backdrop.  If you register the maps as above, you should
be able to patch adjacent raster maps together (you'll want to remove any edges
first). That way you can examine the connectivity.  With the vectors, how you handle
them depends on whether you want the data organized/aligned with each source
scanned map, or whether you want one big vector data set....

Eric G. Miller <egm2 at jps.net>

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