A Study on Digital Orthophoto Generation of Mount Everest Region
1. Introduction
Advancement in digital orthophoto acquisition techniques, lead to continuous growth of orthophoto production. So far none of the tests were performed using digital photogrammetry techniques in an area where the elevation varies (extremely) more than 45% of the flying height above ground level. This study was undertaken as a master thesis program in the university of applied sciences, Stuttgart in collaboration with Z/I imaging, GmbH, Germany. All hardware/software used for the investigation are from the family of ImageStation (joint venture between Zeiss and Intergraph). Here we will, mainly discuss the problems associated with height differences and textures in the images as well as solutions and results. The study area lies on South Asian region and in an antique mountainous country Nepal. Specific area under investigation is the Mount Everest region, well-known highest mountain in the globe, measured from MSL. Curiosity, whether it is possible to perform digital aerial triangulation,
automatic extraction of DTM and orthorectify the images with extreme height differences created by high mountains in the study region, lead to formulate this program. We will address the automatic image matching problems arising from the poor textures in the images and big difference in radiometric resolution. Generation of tie points automatically will be the next issue to be discussed. The orthorectification process for the photographs from Mount Everest region requires not only identified ground control points, but also digital terrain models. Hence a DTM needed to be created as part of study project.
This study project aims to demonstrate how automatic triangulation, extraction of DTM, orthorectification and mosaicking can be accomplished automatically.
The editing of digital terrain model is of great importance, because the data is to be used for the production of orthoimages. To carry out this task efficiently, reference data is required (only map data is available) to ensure that the checks can be carried out on significant areas. The manual selection of checkpoints, is both time consuming and prone to error. This paper starts discussing the data available for the study, methods to be used, problems encountered during operation, solutions so far found out and the results.
2. Data for the Study:
Data available for this study are listed and described in table-1. Data available are panchromatic aerial images at a scale of 1:50000. The nature of terrain is highly irregular topography, from steep to very steep and most of the area is covered with snow. The variation of height within the project area is from 2500 meters to 8848 meters, creating extreme elevation differences of more than 45% of the relative flying height in individual models
