[erdas-l] EGM96 to WGS84 conversion

Emmanuel M. Bina

unread,

Jun 2, 2008, 6:31:06 AM6/2/08

to ERDAS Discussion List

Hi,

I have a quickbird ortho-ready standard image and I wish to orthorectify it using an SRTM DEM. The SRTM data is referenced to the EGM96 model while the quickbird RPC is referenced to the wgs84 ellipsoid. Does erdas automatically convert the the dem to wgs84 ellipsoid when performing orthorectification or do I need to convert it manually before orthorectification so it has the same vertical reference as the quickbird RPC?

Emmanuel
---
You are currently subscribed to erdas-l as: erdas-l-gar...@googlegroups.com.
To unsubscribe send a blank email to leave-29616694-120484586.1d5...@lyris.dundee.net

Tom Lobonc

unread,

Jun 2, 2008, 3:16:31 PM6/2/08

to ERDAS Discussion List

Emmanuel -

You should manually convert your DEM to EGM96 using the
DataPrep->Recalculate Elevation Values tool. There may be a bug where
the actual vertical datum flag is not being updated even though the
elevation values are (saw this in 9.2 SP1). In most cases this should
not matter, but you might want to use Image Info to reassign the EGM96
vertical datum. This doesn't do any point conversion, just updates the
datum field. You can view the datum field with the HFA viewer to check
it.

Tom

-----Original Message-----
From: Emmanuel M. Bina [mailto:eb...@geodata.com.ph]
Sent: Monday, June 02, 2008 6:31 AM
To: ERDAS Discussion List
Subject: [erdas-l] EGM96 to WGS84 conversion

Hi,

I have a quickbird ortho-ready standard image and I wish to orthorectify
it using an SRTM DEM. The SRTM data is referenced to the EGM96 model
while the quickbird RPC is referenced to the wgs84 ellipsoid. Does erdas
automatically convert the the dem to wgs84 ellipsoid when performing
orthorectification or do I need to convert it manually before
orthorectification so it has the same vertical reference as the
quickbird RPC?

Emmanuel
---
You are currently subscribed to erdas-l as: tom.l...@erdas.com.

To unsubscribe send a blank email to

leave-29616694-97310015.48a1...@lyris.dundee.ne
t

---
You are currently subscribed to erdas-l as: erdas-l-gar...@googlegroups.com.

To unsubscribe send a blank email to leave-29619695-120484586.1d5...@lyris.dundee.net

arto.v...@poyry.com

unread,

Jun 2, 2008, 6:23:06 PM6/2/08

to ERDAS Discussion List

EGM96 is a geoid model, actually based on WGS-84. Perhaps http://en.wikipedia.org/wiki/WGS84#Updates_and_new_standards & links there are informative. An EGM96 raster grid can be downloaded too. Geoid heights can be used to convert between orthometric heights (approximately mean sea level) and ellipsoid heights. According to the Geoid Calculators at http://earth-info.nga.mil/GandG/sathtml/, EGM96 applies only to the WGS 84 reference ellipsoid.

Yours sincerely,

Arto Vuorela / Pöyry Environment Oy
P.O. Box 50 (Jaakonkatu 2), 01621 VANTAA, FINLAND
Tel. +358 (0)40 590 7208, Fax +358 (0)10 332 6761, Operator (0)10 33 11

This email and any files transmitted with it are confidential, may be legally privileged and are intended solely for the use of the individual or entity to whom they are addressed. If you are not the intended recipient, please note that any use, distribution, or reproduction of the contents of this email is strictly prohibited and may be unlawful. If you are not the intended recipient, please notify the sender by return email and destroy all copies of the original message including any attachments thereto. Thank you.

Please note that we take reasonable precautions to prevent the transmission of viruses; however, we cannot guarantee that this email or its attachments are free from viruses. We only send and receive emails on the basis that we are not be liable for any loss or damage resulting from the opening of this message and/or attachments.

--- 
You are currently subscribed to erdas-l as: erdas-l-gar...@googlegroups.com

. 
To unsubscribe send a blank email to leave-29621144-120484586.1d5...@lyris.dundee.net

Emmanuel Bina

unread,

Jun 2, 2008, 11:50:41 PM6/2/08

to ERDAS Discussion List

Hi Tom

I couldn't find the EGM96 model in the elevation info chooser. I'm using 9.1

Emmanuel

Emmanuel -

Tom

Hi,

Emmanuel
---
You are currently subscribed to erdas-l as: tom.l...@erdas.com.

To unsubscribe send a blank email to

leave-29616694-97310015.48a1...@lyris.dundee.ne
t

---
You are currently subscribed to erdas-l as: eb...@geodata.com.ph.

To unsubscribe send a blank email to

leave-29619695-95781617.a90c...@lyris.dundee.net
No virus found in this incoming message.
Checked by AVG.
Version: 8.0.100 / Virus Database: 269.24.5/1479 - Release Date: 6/2/2008
7:02 PM

---
You are currently subscribed to erdas-l as: erdas-l-gar...@googlegroups.com.

To unsubscribe send a blank email to leave-29622849-120484586.1d5...@lyris.dundee.net