Georeferencing Image with GDAL

[Sumesh K.C.]

Hello Everyone,

I've been trying to georeference image with GDAL.

I've a number of GCPs (Ground Control Points) that can be easily identified on the image. And what I'm trying is to create a program to georeference image by entering the GCP value on the corresponding point on the image (in terms of rows and columns) without using the stand-alone application i.e. gdal_translate.

I'm trying to do everything for the beginning.

Can anyone guide me, how i should start?

Thank you, in advance!

[Kai Muehlbauer]

Hi Sumesh,

could you be a bit more verbose?

If I got this correct:

1. you have an image where you have no georeferencing
2. you know the coordinates of several points (GCPs)
in the image
3. you want to use these GCPs to reference the georeference the whole image

My questions are:

a. Which format is the image? What is is source (Scan, aerial photo)?
b. Do you know the locations (in terms of rows and columns) or do you
want to identify the points by gui (mouseclick in image)?

Generally this is possible.

Cheers,
Kai

--
Kai Muehlbauer
Meteorological Institute University of Bonn
Auf dem Huegel 20 | +49 228 739083
D-53121 Bonn | kai.mue...@uni-bonn.de

[Sumesh K.C.]

Thanks for the reply Kai!

Yes, you are right. Those 3 points you noted and understood is right.

I have an image in tiff as well as in jpeg format, which is actually an aerial photo. And I have the location of the GCPs in terms of rows and columns.

So, please help me!

[Kai Muehlbauer]

Sumesh,

the main problem with your task is the image source.

Since it is an aerial photo you can't georeference it directly in most
cases due to the inherent perspective projection. So before doing the
georeferencing by GCP the image has to be orthorectified.

Unfortunately I can't provide a simple solution to this.

You might find this StackExchange samples useful:

http://gis.stackexchange.com/questions/644/work-flow-for-georeferencing-imagery-using-open-source-tools

http://gis.stackexchange.com/questions/5487/best-method-to-georeference-oblique-photographs

Also this here at qgistutorials might help you:

http://www.qgistutorials.com/en/docs/advanced_georeferencing.html

Bests,
Kai

>> D-53121 Bonn | kai.mue...@uni-bonn.de <javascript:>

[Sumesh K.C.]

Thank you for the interest, Kai!

Sorry Kai, i didn't illustrate everything that you need to understand.

I'm final year undergraduate student, studying Geomatics Engineering at Kathmandu University, Nepal. I'm doing final year project on the topic "Crop Health Monitoring and Yield Prediction for Precision Farming Through the Use of Low Altitude Remote Sensing". Georeferencing is just the initial important step in the project.

Actually, I've got a dozen of images taken with UAV for my project. Bundle Adjustment was carried out after I acquired the images, so i think the output images after Bundle Adjustment would be ortho-rectified.

I've used circular disk of some radius of unique color, and place it on the ground where the GCPs are located. So, these disk actually means GCPs. From the images, I've extracted those disk and calculated the centroid value which represents the exact location of the GCPs. From this operation, I can get the position of GCPs in terms of rows and columns. Now, I need to georeference with the help of GCPs and the location of GCPs in terms of rows and columns.

Please, will you help me?

If I'm wrong please forgive me. And would you please help me considering that the images I've are ortho-rectified.

Thank you, Kai!

Waiting for reply!