Constructing a GIS using unregistered aerial photos of the Cordillera de San Buenaventura, Volcanic Arc of the Central Andes

Austin BaldwinGIS in Water Resources (minus the “Water”!)

Volcan San Francisco and Incahuasi

22,590 ft.

14,760 ft.

Nevado Ojos del Salado, Argentina/Chile border

Objectives:

1. Create a GIS of the Cordillera de San Buenaventura using:• Roads and International Borders • GTOPO30 Topography• Landsat Satellite Imagery• Rock Sample Waypoints

2. Add unregistered aerial photos to the GIS

Roads and International Borders:Downloaded from the ESRI Geography Network websitehttp://www.geographynetwork.com

GTOPO30 Topographic Information:Downloaded from the USGS website.http://edcdaac.usgs.gov/gtopo30/gtopo30.html

Landsat Satellite Imagery:Downloaded from NASA’s MrSID website.https://zulu.ssc.nasa.gov/mrsid/

Rock Sample Waypoints:50 rock samples were collected in the field, and their locations were recorded using a GPS receiver.

Rock Sample Waypoints:50 rock samples were collected in the field, and their locations were recorded using a GPS receiver.

PART II: Adding aerial photos to the GIS

Problems:

• not orientated in compass directions

• not georegistered

• unknown scale

• geographic distortion

N ?N ?

1 km or 100 km?

Adding aerial photos to the GIS:

Digitizing Surface Features:Air photo resolution is far superior to other imagery sources, such as Landsats or topographic maps.

This high resolution reveals surface features such as faultswhich may be impossible to distinguish in Landsats. With georegistered air photos, these features could be digitized as a layer in ArcMap.

Field Mapping:In the field, knowledge of scale, map orientation, and Easting/Northing is very useful.

Why Bother??

Resolution Comparison between Resolution Comparison between Landsat imagery and air photoLandsat imagery and air photo

Satellite Landsat image Aerial Photo

Another Resolution Another Resolution ComparisonComparison

Satellite Landsat image Aerial Photo

Adding aerial photos to the GIS:Adding aerial photos to the GIS:

The Georeferencing tool allows the user to align- or georeference- data without a coordinate system (i.e., air photos) to a map with a coordinate system.

It is essential that there are physical features visible in the existing map that are also visible in the air photo. For example, road intersections, buildings, or mountain peaks. These common features will be used to “link” the air photo to the map.

Adding aerial photos to the GIS: Adding aerial photos to the GIS:

Start by adding the Start by adding the

unregistered air unregistered air photo photo

to the data frame to the data frame

containing the containing the

existing map. existing map.

On the On the GeoreferencingGeoreferencing

toolbar, select toolbar, select

‘‘Fit to Display’ to Fit to Display’ to bring bring

the air photo into the the air photo into the

field of view with the field of view with the

Landsat.Landsat.

Making a Link between a common Making a Link between a common feature:feature:

Using the ‘Add Control Points’tool, make a link between a feature common to both the air photo and the registered data.

Click a point on theair photo first, thenon the registered data.

Select the Transformation (aka, “rubberization”):

The Transformation Ordercontrols how much the new data will be distortedfor a best fit of the links.

1st Order Polynomial (Affine):To shift, scale, and rotate the image. Only for images with no geographic distortion-Requires 3 links for an exact match.2nd Order Polynomial: Allows some pull and stretch of the image. Requires at least 6 links.

3rd Order Polynomial: Allows maximum amount of stretch and pull of the image for a best fit of the links. Used for images with considerable distortion. Requires at least 10 links.

How well do they match?

GeoregisteredLandsatimage

AerialPhoto

Landsat image Air Photo

Final Product:

High-resolution, georegistered aerial photographs, ready for digitizing or field mapping!

Limitations of this method:Limitations of this method:

• Must have a georegistered layer for Must have a georegistered layer for linking common points. linking common points.

• Resolution of images-Resolution of images- with coarse with coarse resolution it resolution it

is more difficult to pinpoint common locations is more difficult to pinpoint common locations for linking.for linking.

• Geometric Distortion of aerial photos- Geometric Distortion of aerial photos- makes it impossible to align all points. makes it impossible to align all points.

“Orthophotos” correct for this distortion, but “Orthophotos” correct for this distortion, but are costly. are costly.

Muchas Gracias!

Laguna Miscanti, northern Chile