Art409

Hi There. I'm back. Can you give me access to other forums? Regards. Art

Hi Guys, Hi Lurker. After some time away of the geospatial stuff i'm back. ¿could you reactivate my account? Thanks

Hi Mapper310! One question: "Resolution" of what? The same word uses for different tipes of things. In general remote sensing, "resolution" refers to the ability of discrimnate different things. Spatial resoulution, Spectal resolution, Band resolution, Dynamic resolution, time resolution, and goes on...

Thanks Lurker!. I don'y want to sound unpoilte. Sorry if my english limited me in that way pasfan01. The key is that the soft, it's an implementation of some tehoretical algorithm. Sometimes, we coud use or adapt that algorithm for a different prupose, but sometimes... is usefull. Knowing the photogrammetric tehory, I advise that using Agisodt for pushbroom (or barridors like Landsat TM and ETM) CAN'T perform fine. Usually in remote sensig DTM there is not not an inmediate risk for the user, But this sound to me like some one using an enginieering software designed for bridges structural analysys, trying to calculate the dome of a stadium, What I mean with "Can' perform fine"?? I state that the deliverable that you can obtain with cartosat-1 and Agisoft, will be less accurate that any ASTER DTM, OR SRTM (Ok SRTM data was taled in 2000, but Aster is still operative) I'd out of spatial imgining for a couple of years, so I don't know what images are available today. Art PS: If any one want an explanation about why the movement of the camera (180km) is relevant, I can explain that

LOL. Here goes one example of "theoretical stuffs". Why don't try to build a satellite instrument to see earth surface freflectance in ultraviolet o shoter wavelegnghs? Answer: it''s IMPOSSIBLE to see that from space due atmospheric absortion!!! What you call "theoretical stuffs" is the cause that we need the soft. "Discover" dosen't mean "ignore" knowledge. Belive me, maybe the soft allow you to get some result. But these result is a useless. I hope your doctor don't sahre your point o view!

Happy new year!. Agisoft solution is for frames. 1 frame, exterior orientarion (aka Camera in agisoft) A landsat 7 scene got a aprox 180km along track, that menas the camera moved more than 180Km. ¿You took that as a simple scene?

If you found please let us know. I'd looked for months a no result yet.

Very nice Lurker! But i'd go for the Firefly6 Pro! https://www.birdseyeview.aero/ ok. weights lots more, but... poerate from anywhere and productivity is unmatched!

nnico. that's beyond my league, but... whay version of carry map you are working with?

Hi Laura: You want to calculate tree heigths? Or just want a DEM? Some info now: Optical data can't go below trees or any other coverage. You just can use patches with crear view o terrain to extract DEM LIDAR can reach the ground going trough "holes" between foliage, in a way that we can ASSume the last echo as a terrain echo. Very dense foliage don't allow lidar reach ground. Radar... (ouch!) I'n out of date about SAR new satellites, or aerial ones., but: REMEMBER, inside the SAR minimal data (let's call it a PIXEL, for now) you got a lot of responses added from everithing that reflect te signal. Note: Landstat 8 is no good for stereo, so LANDSAT8 discarded for DEMs Art

Landsat-1 (Originally named ERTS-A for Earth Resources Technology Satellite); Landsat-2 (called ERTS-B until few time prior to launch, and Landsat 3; and also Spot (Satellite Pour l’Observation de la Terre: Sattellite for Earth observation) prime focus was in terrestrial natural resurces (soils, crops, etc) Landsat was aimed to for geology an Spot for agriculture) Due communication limitations at that time (we talk about hundreds of megabytes by minute in the ’70s) they chose limitated number of bands to survey different spectral signatures, and due just few things got differences in blue band (beyond water) they chose to carry a more usefull close infrared band than the blue one. Regards. Art

ajaysbharadwaj Nice issue do discuss! A) SOURCE DATA yes, Google Earth uses mostly SRTM, but in someplaces uses other sources. We don't know where or the source quality, so.. we end with a DEM with unknow quality. "NASA has released a void-filled version of the Shuttle Radar Topography Mission digital elevation model, known as "SRTM Plus" or SRTM NASA Version 3. SRTM Plus uses SRTM Version 2 (see below) where the radar interferometric method was successful (not void). Most voids are filled with elevation data from the ASTER GDEM2 (Global Digital Elevation Model Version 2)." (see http://www2.jpl.nasa.gov/srtm/) Bayond that, you can search in your Area of interest for better accuracy/Resolution DEMS Interpolation ============ I strongly disagree with you. You took grid data. get XY points (manually), and then interpolate again to a grid!!! Why don't you just use Shuttle Radar Topography Mission (SRTM) Data in Surfer?? (here go how: http://www.goldensoftware.com/Newsletter/issue52s# ) Contours "look better" because: 1) you use less source data to interpolate (if you are use the more data points you are using interpolated points to interpolate, and if you use the same data ponits you work a lot more for the same results) and most important: 2) You interpolate with a smooth/stocatic method (Kriging), and using default parameters! You can use a lot of interpolation methods (In surfer, ArcGIS, or mostly any software) Linear, IDW, Krigin, NN, Spline, Trend, etc., with o without breaklines/barrers I ussually avoid use Kriging for terrian, beacuse tend to smoth terrian breaks. Why? ¡¡¡Nice and Smooth countous dosn't mean better acuracy!!! Ussually the oposite! Regards Art

Sorry, but I don't understand the advantages over download the full SRTM data. https://lta.cr.usgs.gov/SRTM "SRTM 1 Arc-Second Global elevation data offer worldwide coverage of void filled data at a resolution of 1 arc-second (30 meters) and provide open distribution of this high-resolution global data set. Some tiles may still contain voids. Users should check the coverage map in EarthExplorer to verify if their area of interest is available. Please note that tiles above 50° north and below 50° south latitude are sampled at a resolution of 2 arc-second by 1 arc-second." You can donload fromUSGS's Eart Explorer http://earthexplorer.usgs.gov/ Data is also availabre from other sources, and in other formats Cherrs Art

Hi Lurker! I'm sorry too for the late reply. As you I trying to classify UAV point clouds, and yes, Lidar derivates are different. Lidar got echo numer (or full wave proccesing), and Image derivates got 3 (or more) color bands. My main goal is extract buiding from cloud points, but I'm sure that I'm far behind your steps. I got soid theroetical background, but I almost got not time for test, (and I don't plan to trask/deliver anything 'till I'm not sure of the process) Please take a look to one or both "Lidar analyst" and "feature analyst" Looks promising Art

there is a couple of tools really interestng: Lidar analyst and feature analyst from Overwatch technologies (http://www.vls-inc.com/) So far I can´t test it, but seems one of the best of the market.

Deepgis, I don't think tou could perform that in Agisoft. (sorry pasfans01, but I'm disagree with you) Cartosat-1 is a pushbroom system, not a framed one. That means the camera scan the ground track line by line continuosly, as spatial vehicle move foward in orbit. So, in order to achive results you need camara position for each scan line, more than 10.000 per scene, that means more than 20.000 cameras for agisoft (you need 2 scenes) Besides agisoft search for tie points usin images patchs, and you only could get part of a single line as a patch. Even if (with a miracle) you could make the software go, I don't think you could get any acceptable results, even with very low resolution Use PCI, ENVI or Erdas. lot less painfull, lot better results and the most important: proved solution Art

I'm amased!! just think! with that and ntrip.... rtk on the phone to get what? sub foot or sub decimeter presition? wow!!! Thanks Lurker.!

They use te same principle for 3D recosntruction: Stereovision. They simple calim, "the imagery does not need to be captured as traditional stereo pairs" but they use the stereoscopic pronciple. About GCPs there only 4 options: 1) They got a HUGE base of existants GCPs (or georreferenced images) 2) They got very precise oribital parameters (Similar to classic External Orientation) 3) they got any comercial secret unknow by scientists. 4) they lie (I don't think so) I'll like to add some reference numbers to explain my statement Here goes some numbrers about the need of accurate orbital parameters. A satellite height between 500 and 700km, implies velocities betwen 7.52 and 7.62 Km/s So... if you want satellite position better than 1 meter you need an accurate position 10.000 times by second (no GPS got that rate) So.. we must interpolate positions... Attitude: an error of 1 arc second means at 700 Km, 3.39m (2.42m at 500km), so... we need an attitude accuracy of 1/3" or better... Thats goes for an absolute geolocation of 3meters (despite heigths) Obviously you need attitude data at 10KHz rate (10.000 mesures, by second) Again. we must interpolate. The good news: At those heigths orbits are mostly smooths, and position and attitude changes are not violent, as in an aircraft. The Toutin’s Rigorous RPC Model (Toutin, 2002), was the better choice for that. A good paper on "COMPARISON OF DIFFERENT MATHEMATICAL MODELS ON THE ACCURACY OF THE ORTHORECTIFICATION OF ASTER IMAGERY" could be found here: http://www.isprs.org/proceedings/XXXVI/1-W41/makaleler/OK_Model_ASTER.pdf Art

Stereoscopic Principle involves 2 (or more) images of the same object captured from DIFFERENT positions. for presition is very importante the Base/Heigth ratio (Base: distance between images; heigth: Distance from image to object) In classic aerial photogrammetry a good B/H ratio round 0.6 The case of multiple "Very High Resolution satellite imagery (not stereo)" cited by intertronic, could obtain poor results due B/H ratio. Modern Photogrammetric techniques adresses ray-cloud photogrammetry, that (in very simplified words) involve several images of the same object (and several correlations), but this is not apllicable yet to satellite images. Aster images offers a good B/H ratio, (I belive is close to 0.6, but not sure). Process is relatively simple in some softwares. But I don't recall any modeule to do this in ArcGIS: Good option for software for this are: PCI Geomática, ASTER DTM (for ENVI); ENvi with DTM module, Erdas. You can also download ASTER DEM Products from the web. Final TIP: The use GCPs (Ground Control Points) IS VERY IMPORTANT. If you can't afford get them on field with a GPS (differential GPS), you can donwnload a Envi processed Image and a DEM, so use some ponts from that dataset. Regards Art

It depends on the objective of your map. For navigation is better that you use LWS (because if anybody in a boat reads in the map i.e 3 meters, the water below has a minimum of 3 meters deep; otherwise he/she coud read 3 meters, and hit the bottom and sink ´cause there is 1 meter of deep) On the other side, if you use MSL, please adda a big "Not Intended for navigation" Regards. Art