Latest Contributions by LaszloKomaromi2

‎03-06-2017

This sounds way too complicated. Almost makes it impossible to align DEMs. I started to question the precision of every DEM I ecer used.thanks for your help Dan

‎03-05-2017

Apparently, my contour map can only be projected in WGS 84 UTM Zone 27N. WGS 84 projection is not working. Other than that, my three DEMs were in different formats and spatial resolution. I resampled them, but changing formats result in different elevation values. It is very important to have them right since I am looking at volumetric differences of glaciers through geodetic mass balance method. According to the volume calculations using 'Surface volume' tool, my 2004 DEM shows an increase in volume compared to the 1986DEM. It is unlikely that the glacier has grown since, as ice is known to be retreating rapidly in that region. It bugs me that when changing formats and/or pixel type the elevation values and volue changes. It makes me wonder what the actual elevation values are for my DEMS.

‎03-04-2017

Very true. I double check the above. Thanks.

‎03-04-2017

I switched off background geoprocessing. The overall performance seems to have improved but I got the same error message while projecting raster.

‎03-04-2017

That's right, but it doesn't explain why the contour maps don't draw. They are in the same projection. Also, I tried the above Project Raster tool. Usually I get error messages when performing tasks for no apparent reason. Here is the latest one when trying to project raster:

‎03-04-2017

Hi Chris, Its not the cells size, they are all in agreement. I'll try the Snap Raster though, however, looking at properties, all my DEMs are identical, from cell size through pixel type and format. I'll keep on experimenting. Thanks a lot, Laszlo

‎03-04-2017

Hi Dan, Thanks for your reply. I resapmled my DEMs to the same resolution(25x25m) before processing them. I have defined the spatial extent myself, by clipping the DEMs to a vector outline through the Image Analysis menu. My other problem is that when I turn these three DEMs into contour maps two of them doesn't draw. I have imported the third DEM's Coordinate system, also the 'project' tool and tried several other systems, nothing works, whereas they all show up correctly before turning them into contour maps. Ideally, all layers should be in the same coordinate system, but somehow it is just not possible in my case. For instance, my vector files are in 1993 Lambert system and my Landsat images are in WGS 1984. They perfectly overlap this way, but if I change my vector to WGS 1984 it won't draw. I have been using ArcMap actively for a year by now, performing different tasks but i still can't figure out why this is happening. Any idea? Many thanks, Laszlo

‎03-03-2017

Hi everyone, I would like to compare the elevation and volume of three DEMs. When I export the original DEMs in TIFF format the elevation values change. I do not use compression or any other kind of data transformation. It makes me wonder what the real elevation values are. Before After My second question is that I have calculated the volume difference of my DEMs (not the TIFF versions but the original) and it says that there is an increase in total volume between the DEMs. It is nearly impossible, since these are glacier surfaces that are known to decline in this area (and in most parts of the World). It is unlikely that there is a snow bias and my DEMs are in the same coordinate system and all clipped to the same vector shape. Any idea what could have gone wrong? Thanks Laz

‎01-21-2017

When trying to align two raster layers I import the spatial reference of one image to the other. The result is a layer that either never draws or not overlapping the other layer. It happened thousands of times and I am wondering why. Any idea?

‎12-29-2016

I am classifying glaciers using the iso cluster unsupervised classification tool. However, parts of the glaciers are missing due to debris and shadow. Since my composite images(Landsat TM bands 2,4,5) clearly distinguish ground from ice I use them as backrgound layer to correct the partial misclassification using on-screen digitising (I found the 'reshape tool' the most useful editing function for this task). In order to be scientifically correct I should use ground truth for each image for each year in the same month when the image was acquired. Since this is clearly impossible my question is how do spatial analyst experts solve this problem. This is the only way to classify ice extent for my images, therefore I feel like it is a Catch 22 of remote sensing analysis.

‎12-18-2016

My idea is to use the existing 'gap mask' layer provided by the USGS for each image as input raster for unsupervised classification. This will leave me with two classes: data and no data. I save the no data class (which represents the error gap itself) as a new layer and I transform it into a polygon layer. I use this new layer to cut the original image in order to get rid off the stripes in the image. I chose another imagebfrom the same day or week and use it as a background for the other image. Missing gaps will be filled this way since stripes don't overlap between two images. Since there shouldn't be significant topographic difference between two images when collected within the same week or so , blending them this way seems reasonable. I don't know if this method has ever been used, I just thought it would be a logical way to fill the gaps as I need data between 2003 and 2012 for my dissertation. Other satellite imagery is not available for my area for this period Any thoughts on this method? Thanks in advance. Laz

‎12-02-2016

Hi there, I am about to classify Landsat images using unsupervised classification. I have 16 images (1 image/year) from which I intend to extract glacier surfaces only. The first step would be to create composite images consisting the relevant bands for each year. My question is which bands should I combine from each Landsat scenes to get a composite image that can be used as input raster for unsupervised classification? I am looking at the 30m resolution bands only. Here are the band designations for each satellite: What are the band designations for the Landsat satellites? Thanks for your help in advance. Laz

‎11-12-2016

I see your point but currently I need to save time because I have 4 months to finish my dissertation. It sounds enough but I work full time and I need to look up many of these baby steps on Esri or other websites. I do study GIS but not remote sensing so that I need more practice in this field. I will see how difficult it is to cloud mask rasters and try do do so. Even if I don't I will end up with about 25 images that is not that bad. Would you also recommend combining two images in Landsat 7 to fill the error gap? I appreciate your help.

‎11-12-2016

Thanks Dan. Surely, but in some case there are more visible bands. I have chosen images from August and September only so that its the end of melt season and there is no snow in the pictures. I am looking at the period between 1984 and 2016 with few years gaps because of clouds and the Landsat 7 error. However, I have some images with minor clouds that I should consider. I am not sure if I should mask them or If I am going to have time for that as my dissertation is quite complex.

‎11-12-2016

Yes, this seems to be a basic question but I haven't found useful info on the web.

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My Ideas

Latest Contributions by LaszloKomaromi2

Re: DEM values/DEM differencing

Re: DEM values/DEM differencing

Re: DEM values/DEM differencing

Re: DEM values/DEM differencing

Re: DEM values/DEM differencing

Re: DEM values/DEM differencing

Re: DEM values/DEM differencing

DEM values/DEM differencing

Aligning rasters

How do I get ground truth for a 30 years time series when using on-screen digitising method?

I was wondering if its a scientifically correct method to remove data gaps from Landsat 7 SLC off images.

Unsupervised classification

Re: Which bands of the Landsat family should I use to analyse ice caps?

Re: Which bands of the Landsat family should I use to analyse ice caps?

Re: Which bands of the Landsat family should I use to analyse ice caps?