So I work with Forestry guys and we
do some very similar things when georeferencing. You need a good
point spacing - and typically I describe that as a point at each
coner of the image you are going to georeference plus one for
the middle or (sorry for using this example but they have really
good docs) -
http://webhelp.esri.com/arcgisdesktop/9.2/index.cfm?TopicName=Georeferencing_a_raster_dataset
If it were me I would do this:
1. go to USDA Datagateway -
http://datagateway.nrcs.usda.gov/
- and download a NAIP image of your Area (sorted by county). It
will be sid format (probably) - so if you are on windows you
should be OK for opening up the image.
2. Use that to georeference the Google earth Screenshot. It will
give you a lot more control points than just your GPS.
- GPS can be notorious for not quite being right if you
didn't way point average - my forestry guys GPS property
corners and that makes me not happy every time they do it.
- Both Google and Bing are good and the open layers plugin
rocks - but - both image layers aren't captured (at least to
me) with mapping in mind - i.e. they may be questionable.
OR
1. Download the GPX data from your unit using either QGIS or DNR
GPS
2. Convert to shapefile.
3. Create your contours there using a new shapefile (digitize
them in again).
I know I just glassed over a ton of technical by doing a 1 2 3
type scenario but I think (just my opinion) there's more hair
pulling than you need to be experiencing (For the record I'm
bald so I know all about hair pulling).
Yell if you need more help either off list or on list - I hope
some of this at least pushes you in a good direction.
Randy
-----------------
Randal Hale, GISP
North River Geographic Systems, Inc
http://www.northrivergeographic.com
423.653.3611 [email protected]
<mailto:[email protected]>
twitter:rjhale
http://about.me/rjhale
On 02/05/2014 12:04 PM, Mike Keelan wrote:
Thanks James,
I got through the geo-referencing operation and it did
generate a new modified layer based on my .jpg. However the
new layer is badly distorted/stretched, (I used 4 coordinate
Garmin GPS reference points), and it is not in the right
location. I can only find it by zooming to that layer
extent. I'm wondering if my coordinate data from my Garmin is
consistent with what the geo-referencing program uses? My
Garmin data is xx.xxxxxx and it uses negative numbers to
represent East instead of West. Or, might there be an
accuracy issue?
I know my Garmin way-point data is good because it overlays on
my Ortho almost perfectly as a separate layer.
Mike K
On 2/3/2014 8:28 PM, James Wood wrote:
Mike,
Here is a good tutorial overview of the georeferencing tool
in QGIS:
http://qgis.spatialthoughts.com/2012/02/tutorial-georeferencing-topo-sheets.html
If the image is not in coordinate space, it will not line up
with your other data. so this operation will be necessary.
Also, just as a side, I would think that an export from
Powerpoint would degrade image quality (depending on the
original). I would look at and maybe try for future use The
Gimp (which is an open source, free Photoshop-type
application). It will give you more control on export of not
only various output formats but also pixel and color depth,
and the like. The official site is
http://www.gimp.org/.
Best Regards,
James
Date: Mon, 3 Feb 2014 19:59:14 -0500
From:
[email protected]
To:
[email protected];
[email protected]
CC:
[email protected]
Subject: Re: [Qgis-user] How do I register a Google Map?
OK, I installed the Open
Layers plugin and it works very nice but it won't do
what I need, so let me be more specific and see if there
might be a remedy.
The contour lines that I want were actually obtained
using a hand held Garman GPS. The Garman data was
overlaid on the Google map, (with water depths),
special integration, then that map was exported as a
Jpeg, then imported to PowerPoint where a visual
interpolation was done to make the final set of contour
lines for the various lake water depths.
My desire is the digitize these contour lines as
a set of separate layers. ie 5' deep, 10' deep, etc.
There are many good uses for these layers, but they
must be accurate as to location and size. I don't think
I necessarily need spacial info on the "map"/Jpeg if I
can get the whole map in the right position, and size,
so I can do the digitizing (which would then have the
spacial info). Then I can discard the Jpeg.
Is it hopeless?
Mike K
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